Have a single blur implementation

After experimenting with both Gaussian and Kawase, we concluded
that Kawase has similar visuals and better performance.

This CL removes GaussianBlurFilter and promotes KawaseBlurFilter
to just BlurFilter.

Bug: 149792636
Test: librenderengine_test
Test: visual
Change-Id: I6d5790b2735754b5a39dd7367280871ab43f723c