Remove unused SkRRectsGaussianEdgeMaskFilter #include

SkRRectsGaussianEdgeMaskFilter is going away in Skia (https://skia-review.googlesource.com/c/skia/+/121960 (rm SkRRectsGaussianEdgeMaskFilter)) but this usage needs to be cleaned up first

Test: does it compile?
Change-Id: I489123a32958ada2d27425d78b3abb2db2290ce8