Only need GLuints now for GLsyncs.

Bug: angleproject:3611
Change-Id: Id8b11851d8d5d30e6743433c772b9fa85eb875f5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1783406Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>