I installed the WPMU DEV plugin, I did not want it after

Hi,

I installed the WPMU DEV plugin, I did not want it after using it for a bit and removed it.

Will I ever be forced to use the WPMU DEV plugin?

Or will I always be able to install any plugin's with the WPMU DEV plugin?

Also, how do I stop the error message in the backend of my wordpress, because I no longer have the dev plugin?

Thanks!

PS: I am test driving the e-newsletter. With a membership can I install any plug in and theme on any website I develop with wordpress?