w6c: delete unwired backend pass seams

cmd/w6c/cgen.c

@@ -17683,6 +17683,3 @@ cg_file(Cg *c, FILE *out, Node *file)
 	emit_defs(c, out, file);
 	emit_lets(c, out, file);
 }
-
-void	peephole(Cg *c) { (void)c; }
-void	regalloc_init(Cg *c) { (void)c; }