Remove inclusion of repositories.config

If you use package restore, you actually don't want this file
included. It's not needed. It's only needed if you version
packages. AKA, you only need this file if you are not ignoring
the "packages" folder.

VisualStudio.gitignore

@@ -92,7 +92,6 @@ publish/
 # NuGet Packages Directory
 ## TODO: If you have NuGet Package Restore enabled, uncomment the next line
 #packages/
-!packages/repositories.config
 
 # Windows Azure Build Output
 csx