Remove GetIBusKeyCode function that is no longer referenced from
anywhere anymore.

BUG=283612

Review URL: https://codereview.chromium.org/174663003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252916 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252916