Remove theme/default_x00_percent/osx folder.

It's unused, the assets in theme/default_x00_percent/mac are used instead.

BUG=317415

Review URL: https://codereview.chromium.org/68223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234190 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234190