Move CODEOWNERS to .github folder

Since we now have a `.github` folder for issue templates, we can move `CODEOWNERS` to it.

Author: ahoppen

CODEOWNERS renamed to .github/CODEOWNERS

@@ -8,8 +8,4 @@
 # Order is important. The last matching pattern has the most precedence.
 
 # Owner of anything in SourceKit-LSP not owned by anyone else.
-# N: Ben Langmuir
-# E: [email protected]
-# N: Alex Hoppen
-# E: [email protected]
 * @benlangmuir @ahoppen