Remove occluder feature from blur mask filter

AFAICT none of our clients are using this feature

This will change the occludedrrectblur GM.

Change-Id: I7e5b8fa67db0373dee11a1467d2b2b6a414a1574
Reviewed-on: https://skia-review.googlesource.com/147561
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
8 files changed