Revert "Create wrapper around Shader native implementation"

This reverts commit fc42a99e.

Because we are moving away from a wrapper class to delegate
between SkImageFilter and SkShader and instead adding
RenderEffect on RenderNode, this wrapper implementation
is no longer necessary. There are some behavioral
differences between SkShader and SkImageFilter that
would lead to additional complexity in conversions
between these objects and potential bugs.
To simplify this, RenderEffect will be added
directly to RenderNode to support better
caching of rasterization layers that is necessary
for various visual effects like blur.

Test: N/A
Change-Id: I65dc9f8bd26aed8761af13491ae3f6d583208377