Revert "i965/fs: Predicate byte scattered writes if needed"

Revert "i965/fs: Predicate byte scattered writes if needed"

This reverts commit a4031bdfa927fb4c3c5d0bdadc70634f3c1a5eac.  It's
redundant with the sample mask predication done at this point by the
common logical send lowering infrastructure, and rather buggy because
it wasn't applying the correct sample mask in shaders using discard,
since the dispatch mask returned by FS_OPCODE_MOV_DISPATCH_TO_FLAGS
doesn't reflect samples discarded by the shader, so it could have led
to data corruption in fragment shader invocations that execute discard
based on a non-dynamically uniform condition.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>