nir: Return a cursor from nir_instr_remove

Because nir_instr_remove is an inline wrapper around nir_instr_remove_v,
the compiler should be able to tell that the return value is unused and
not emit the extra code in most cases.

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

src/compiler/nir/nir.c

@@ -1159,7 +1159,7 @@ remove_defs_uses(nir_instr *instr)
    nir_foreach_src(instr, remove_use_cb, instr);
 }
 
-void nir_instr_remove(nir_instr *instr)
+void nir_instr_remove_v(nir_instr *instr)
 {
    remove_defs_uses(instr);
    exec_node_remove(&instr->node);