clean up some SkRasterPipelineBlitter TODOs

 1) remove the note about maybe implementing bitV()... we have.
 2) rename append_load_d() to append_load_dst() to match how the
    stages are named (a long time ago they used to end with _d...)
 3) move unpremul handling to append_load_dst() and append_store()
    to make it a bit easier to see how they nest with sRGB
 4) remove append_blend()... it's now just SkBlendMode_AppendStages()

Change-Id: Ic3280b66d8c1f26ef18a55044392f7d18fc29a75
Reviewed-on: https://skia-review.googlesource.com/42280
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed