There are only a handful of SkFlattenables that are not flattenable. That
there are any seems highly illogical. To make this look less like a normal
thing, this removes both macros that marked SkFlattenables as non-flattenable
(in slightly different ways).
The handful of SkFlattenables in our codebase that can't be flattened now
assert violently that they can't be flattened. They're internal or
part of animator... places where we'll never actually flatten them.
TestLooper and DummyRasterizer were so trivial that I just made them flattenable.
BUG=skia:
Review URL: https://codereview.chromium.org/841753002
7e44bb1916