Fold directFilterRRectMaskGPU into directFilterMaskGPU

Change-Id: Id4b636ea305c7cb28dd5efe139d3410f17177f42
Reviewed-on: https://skia-review.googlesource.com/148982
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed