Remove executable bit from several source files in css/

I tried to remove this in my last change, but failed.

Not sure if git-svn can actually do this removal
or if I need an svn checkout.

TBR=abarth
BUG=330389

git-svn-id: svn://svn.chromium.org/blink/trunk@164356 bbb929c8-8fbe-4397-9dbb-9b2b20218538