Remove unused WebKit.gypi

This file is not referenced by the build system. This data is in
Source/web/web.gypi instead.

R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/21128003

git-svn-id: svn://svn.chromium.org/blink/trunk@155115 bbb929c8-8fbe-4397-9dbb-9b2b20218538