w6a: drop chained-ptr-write workaround (c5f30f2 unblocked it)

selfhost/cmd/w6a/parse.ww

@@ -354,13 +354,7 @@ fn addprog(a: *asm_, opc: i32, lbl: str) *aprog = {
 	pr.from = amalloc(a.a, 48u64): *aoperand;
 	pr.to   = amalloc(a.a, 48u64): *aoperand;
 	if (a.head == nil) { a.head = pr; }
-	else {
-		// `a.tail.link = pr` would be a chained-dot write through a
-		// pointer field, which the C cgen we bootstrap on doesn't
-		// support (silently drops the store). Bind a local first.
-		let tail: *aprog = a.tail;
-		tail.link = pr;
-	};
+	else { a.tail.link = pr; };
 	a.tail = pr;
 	return pr;
 };