How can I safely delete references to a plugin that is no longer there?

I deleted a plugin called MailPoet, it was formally called WYSIJA and when I search my database for 'wysija' several records come up which mean that it was not completely uninstalled. Specifically, the relics of this plugin seem to be causing problems for the User Roles across my multisite.

I am trying to perform surgery and remove all instances of this plugin in my database. The record wp_user_roles in table wp_options is my prime suspect. How can I remove the wysija reference in this record?

a:10:{s:13:"administrator";a:2:{s:4:"name";s:13:"Administrator";s:12:"capabilities";a:106:{s:13:"switch_themes";b:1;s:11:"edit_themes";b:1;s:16:"activate_plugins";b:1;s:12:"edit_plugins";b:1;s:10:"edit_users";b:1;s:10:"edit_files";b:1;s:14:"manage_options";b:1;s:17:"moderate_comments";b:1;s:17:"manage_categories";b:1;s:12:"manage_links";b:1;s:12:"upload_files";b:1;s:6:"import";b:1;s:15:"unfiltered_html";b:1;s:10:"edit_posts";b:1;s:17:"edit_others_posts";b:1;s:20:"edit_published_posts";b:1;s:13:"publish_posts";b:1;s:10:"edit_pages";b:1;s:4:"read";b:1;s:8:"level_10";b:1;s:7:"level_9";b:1;s:7:"level_8";b:1;s:7:"level_7";b:1;s:7:"level_6";b:1;s:7:"level_5";b:1;s:7:"level_4";b:1;s:7:"level_3";b:1;s:7:"level_2";b:1;s:7:"level_1";b:1;s:7:"level_0";b:1;s:17:"edit_others_pages";b:1;s:20:"edit_published_pages";b:1;s:13:"publish_pages";b:1;s:12:"delete_pages";b:1;s:19:"delete_others_pages";b:1;s:22:"delete_published_pages";b:1;s:12:"delete_posts";b:1;s:19:"delete_others_posts";b:1;s:22:"delete_published_posts";b:1;s:20:"delete_private_posts";b:1;s:18:"edit_private_posts";b:1;s:18:"read_private_posts";b:1;s:20:"delete_private_pages";b:1;s:18:"edit_private_pages";b:1;s:18:"read_private_pages";b:1;s:12:"delete_users";b:1;s:12:"create_users";b:1;s:17:"unfiltered_upload";b:1;s:14:"edit_dashboard";b:1;s:14:"update_plugins";b:1;s:14:"delete_plugins";b:1;s:15:"install_plugins";b:1;s:13:"update_themes";b:1;s:14:"install_themes";b:1;s:11:"update_core";b:1;s:10:"list_users";b:1;s:12:"remove_users";b:1;s:9:"add_users";b:1;s:13:"promote_users";b:1;s:18:"edit_theme_options";b:1;s:13:"delete_themes";b:1;s:6:"export";b:1;s:17:"wpt_twitter_oauth";b:1;s:18:"wpt_twitter_custom";b:1;s:18:"wpt_twitter_switch";b:1;s:13:"wpt_can_tweet";b:1;s:16:"wysija_theme_tab";b:1;s:16:"wysija_style_tab";b:1;s:22:"wysija_stats_dashboard";b:1;s:19:"edit_wpp_properties";b:1;s:17:"edit_wpp_property";b:1;s:26:"edit_others_wpp_properties";b:1;s:19:"delete_wpp_property";b:1;s:22:"publish_wpp_properties";b:1;s:19:"manage_wpp_settings";b:1;s:21:"manage_wpp_categories";b:1;s:21:"manage_wpp_admintools";b:1;s:22:"gravityforms_directory";b:1;s:32:"gravityforms_directory_uninstall";b:1;s:20:"edit_wiki_privileges";b:1;s:17:"create_newsletter";b:1;s:15:"save_newsletter";b:1;s:15:"send_newsletter";b:1;s:17:"delete_newsletter";b:1;s:23:"create_newsletter_group";b:1;s:21:"edit_newsletter_group";b:1;s:23:"delete_newsletter_group";b:1;s:23:"change_newsletter_group";b:1;s:23:"view_newsletter_members";b:1;s:21:"add_newsletter_member";b:1;s:22:"edit_newsletter_member";b:1;s:24:"delete_newsletter_member";b:1;s:17:"add_members_group";b:1;s:20:"delete_members_group";b:1;s:24:"save_newsletter_settings";b:1;s:25:"view_newsletter_dashboard";b:1;s:25:"import_newsletter_members";b:1;s:18:"install_newsletter";b:1;s:20:"uninstall_newsletter";b:1;s:14:"ure_edit_roles";b:0;s:16:"ure_create_roles";b:0;s:16:"ure_delete_roles";b:0;s:23:"ure_create_capabilities";b:0;s:23:"ure_delete_capabilities";b:0;s:18:"ure_manage_options";b:0;s:15:"ure_reset_roles";b:0;}}s:6:"editor";a:2:{s:4:"name";s:6:"Editor";s:12:"capabilities";a:35:{s:17:"moderate_comments";b:1;s:17:"manage_categories";b:1;s:12:"manage_links";b:1;s:12:"upload_files";b:1;s:15:"unfiltered_html";b:1;s:10:"edit_posts";b:1;s:17:"edit_others_posts";b:1;s:20:"edit_published_posts";b:1;s:13:"publish_posts";b:1;s:10:"edit_pages";b:1;s:4:"read";b:1;s:7:"level_7";b:1;s:7:"level_6";b:1;s:7:"level_5";b:1;s:7:"level_4";b:1;s:7:"level_3";b:1;s:7:"level_2";b:1;s:7:"level_1";b:1;s:7:"level_0";b:1;s:17:"edit_others_pages";b:1;s:20:"edit_published_pages";b:1;s:13:"publish_pages";b:1;s:12:"delete_pages";b:1;s:19:"delete_others_pages";b:1;s:22:"delete_published_pages";b:1;s:12:"delete_posts";b:1;s:19:"delete_others_posts";b:1;s:22:"delete_published_posts";b:1;s:20:"delete_private_posts";b:1;s:18:"edit_private_posts";b:1;s:18:"read_private_posts";b:1;s:20:"delete_private_pages";b:1;s:18:"edit_private_pages";b:1;s:18:"read_private_pages";b:1;s:13:"wpt_can_tweet";b:1;}}s:6:"author";a:2:{s:4:"name";s:6:"Author";s:12:"capabilities";a:11:{s:12:"upload_files";b:1;s:10:"edit_posts";b:1;s:20:"edit_published_posts";b:1;s:13:"publish_posts";b:1;s:4:"read";b:1;s:7:"level_2";b:1;s:7:"level_1";b:1;s:7:"level_0";b:1;s:12:"delete_posts";b:1;s:22:"delete_published_posts";b:1;s:13:"wpt_can_tweet";b:1;}}s:11:"contributor";a:2:{s:4:"name";s:11:"Contributor";s:12:"capabilities";a:6:{s:10:"edit_posts";b:1;s:4:"read";b:1;s:7:"level_1";b:1;s:7:"level_0";b:1;s:12:"delete_posts";b:1;s:13:"wpt_can_tweet";b:1;}}s:10:"subscriber";a:2:{s:4:"name";s:10:"Subscriber";s:12:"capabilities";a:2:{s:4:"read";b:1;s:7:"level_0";b:1;}}s:13:"bbp_keymaster";a:2:{s:4:"name";s:9:"Keymaster";s:12:"capabilities";a:0:{}}s:13:"bbp_spectator";a:2:{s:4:"name";s:9:"Spectator";s:12:"capabilities";a:0:{}}s:11:"bbp_blocked";a:2:{s:4:"name";s:7:"Blocked";s:12:"capabilities";a:0:{}}s:13:"bbp_moderator";a:2:{s:4:"name";s:9:"Moderator";s:12:"capabilities";a:0:{}}s:15:"bbp_participant";a:2:{s:4:"name";s:11:"Participant";s:12:"capabilities";a:0:{}}}

Each subsite has a similar record so I will need to repeat the solution for each.