Remove .idea folder from VisualStudio

Conflicts with JetBrains.gitignore. Some files in this directory should be checked in.

Not sure about *.sln.iml, so I'm leaving that. The JetBrains.gitignore file contains commented-out IML stuff with instructions on when to uncomment.

VisualStudio.gitignore

@@ -384,5 +384,4 @@ FodyWeavers.xsd
 *.msp
 
 # JetBrains Rider
-.idea/
 *.sln.iml