Revert "st/pbo: use cso_set_vertex_buffers_and_elements() for st_pbo_draw"

Revert "st/pbo: use cso_set_vertex_buffers_and_elements() for st_pbo_draw"

cso_set_vertex_buffers_and_elements shouldn't be used between cso_save
and cso_restore because it can switch for cso_context to u_vbuf and vice
versa. Also, ẗhe preferred order of calls for future VB+draw merging would
be set_vertex_elements followed by set_vertex_buffers.

This reverts commit 33e117ed7f3c48d3dbeda9a28603a121eac7a860.

Fixes: 33e117ed7f3c48d3dbeda9a28603a121eac7a860
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4674

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10342>