Remove unreleased BlurShader API

Remove BlurShader API which was part of the initial
implementation blur that internally mapped between
SkImageFilter and SkShader. Because we migrated
away from this approach to leverage SkImageFilter
directly as part of the RenderEffect API, BlurShader
is no longer applicable and consumers should use
RenderEffect.createBlur instead.

fixes: 180766802
Test: builds
Change-Id: Ibbe6360c66b8e3718cac4516130336f5758cbd3e