remove unused flag SK_SUPPORT_LEGACY_COLORFILTER_FILTERSPAN

Bug: skia:
Change-Id: I884f79f9a162f38365930d1ccca889fca2850557
Reviewed-on: https://skia-review.googlesource.com/21202
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
3 files changed