How to remove "This is a child theme of xyz theme"


1. I use child themes for all the themes in my network.

But in theme preview it displays a message

"This is a child theme of Stargazer."

Is there a mu-plugin way to hide this message for all the child themes?

2. In, do you use child themes? If not,how do manage the footers "Powered by" "Theme by" etc etc for various themes?