Remove unnecessary DEPS exceptions

We've cleaned up these dependencies. We can now remove these exceptions from
core/platform's DEPS file.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/40463004

git-svn-id: svn://svn.chromium.org/blink/trunk@160489 bbb929c8-8fbe-4397-9dbb-9b2b20218538