[skif] Remove legacy blur implementation

Bug: b/294100597
Bug: b/40040586
Change-Id: I748de092df18d250dbe5de1fd010819ed6d1320d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/750597
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
3 files changed