[skif] Remove legacy MatrixConvolution code

Bug: b/263137789
Bug: b/40040586
Change-Id: I5ae7a4a0342d1c2686be63b2f31707d567eefaf9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/743096
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed