cut out the rest of blend modes in flutter

SkXfermode_opts.h is moot when SK_FORCE_RASTER_PIPELINE_BLITTER is
defined.  There are a couple other blitters and routines and things
that are also just there for 565/8888 performance, so I think we
can just turn on SK_FORCE_RASTER_PIPELINE_BLITTER and start guarding
the rest of them similarly.

Looks like maybe cuts another 13K?

Change-Id: Ib3894b07da649a93e93b6a4cb7686772a57b6def
Reviewed-on: https://skia-review.googlesource.com/c/164181
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed