eliminate srcover_bgra_8888

It's the same as swap_rb -> srcover_rgba_8888.

Change-Id: I1849ecce6efd317a37c9640cc283b812cb23cd6d
Reviewed-on: https://skia-review.googlesource.com/c/163172
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed