Make deferred render target context without config or format

config is completely redundant. No caller really cares what the backend
format is.

Change-Id: I93f1feb3ee61db6c21b7915bab3ee3fba5656f92
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/225194
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
55 files changed