remove obsolete SK_SUPPORT_LEGACY_SCALARMUL code

Bug: skia:
Change-Id: Ifdff1af7fc6b8cd6db77e4afd9794b11011cc31e
Reviewed-on: https://skia-review.googlesource.com/12242
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed