Remove support for Dawn in Ganesh.

Bug: b/297077133
Change-Id: Ic0c5bd604adbc9e485b545b7d09818be783e4bed
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/746783
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
81 files changed