Fix a couple forward declares in angletypes.h. These were vestigal from previous code. BUG=angleproject:1593 Change-Id: I1d9a8e6f60d1dadf8a8a598bdbddd98457eb559c Reviewed-on: https://chromium-review.googlesource.com/442651 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>