gallium/aux: remove unused u_blit.[ch]

There's no users of this code, so we might as well get rid of it to
avoid confusion with u_blitter.[ch].

Acked-by: Jose Fonseca <jfonseca@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6651>
4 files changed