You don't want to let Microsoft own your projects, right? Thank you for your support (of Open Source).
Before the Microsoft acquisition: The source code on GitHub was open, meaning visible to anyone. Including to Microsoft. The ownership of the source was with whoever held the copyright. If I posted something on GitHub with one of the standard FOSS licenses (say the BSD license), then anyone (including Microsoft) could use it, but they could not prevent others from using it, nor could they pretend that they owned the copyright.
After the MIcrosoft acquisition: The source code on GitHub is open, meaning visible to anyone. Including to Microsoft. The ownership of the source is with whoever holds the copyright. If I post something on GitHub with one of the standard FOSS licenses (say the BSD license), then anyone (including Microsoft) can use it, but they can not prevent others from using it, nor can they pretend that they own the copyright.
Now explain to me why you want to remove your code from GitHub? Because you don't want MicroSoft to show you ads when you look at your source code, and so on? You prefer to see ads shown to you by other companies when you use a free service, which is paid for by showing you ads?
If you hate Microsoft so much, here is a proposal: Post your extremely valuable and useful source code somewhere, but give it a specially modified license, which allows anyone to look at it and use it, but not Microsoft. Oh wait, you probably also hate other companies (Facebook? Oracle? Google? Amazon? your local phone company?), so your license will have a long list of excluded companies. Oh wait, you don't even know which companies you hate; for example, in that list we forgot Uber, Tesla, and your local electrical company. So write a license that requires anyone to first ask you for permission to look at or use your software, so you can decide in each case whether you hate the company or not. Oh wait, people might ignore your license and look at the software even if you hate them and you read your source even when they are not supposed to. Easy to fix: just don't post your software at all, and keep it secret, only visible to yourself.
if you believe in FOSS (remember, the first two letters stand for Free and Open), then that means free and open even to the people you don't like.