lima/ppir: remove assert on ppir_emit_tex unsupported feature

lima/ppir: remove assert on ppir_emit_tex unsupported feature

This assert causes testing tools such as shaderdb to abort on some test
cases. This is an unsupported feature and not a compiler bug. The
compilation error is already propagated correctly, so we can remove the
assert to allow testing tools to run to completion.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3176>