This removes the format type parameter from places where it isn't
needed. It also removes the 'write color' functions map. This map was
redundant with the angle::Format write function.

Bug: angleproject:2729
Change-Id: I24e4548a89342237d7ed25180fea156fba51ccab
Reviewed-on: https://chromium-review.googlesource.com/1142300
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>