Revert "Add .gitignore to the /skins directory"

New skin files (images etc.) seem to be matches by these
rules. I'm going to revert this for now since it's annoying,
feel free to resubmit a .gitignore that works.

This reverts commit d21381021658079720ce1a9aa9f0e989d8dd358e.

Change-Id: I77655ea4ba3ddb5941e1e423ad766be20479247f
Merge "Revert "Add .gitignore to the /skins directory""