nir: make cleanup_cf_node() not use remove_defs_uses()

nir: make cleanup_cf_node() not use remove_defs_uses()

cleanup_cf_node() is part of the control flow modification code, which
we're going to split into its own file, but remove_defs_uses() is an
internal function used by nir_instr_remove(). Break the dependency by
making cleanup_cf_node() use nir_instr_remove() instead, which simply
calls remove_defs_uses() and then removes the instruction from the list.
nir_instr_remove() does do extra things for jumps, though, so we avoid
calling it on jumps which matches the previous behavior (this will be
fixed later in the series).

Signed-off-by: Connor Abbott <connor.w.abbott@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>