clean up SK_LEGACY_4F_XFERMODES

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I3f41510f00211849b80ff121f5b18354174108c4
Reviewed-on: https://skia-review.googlesource.com/c/163173
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed