gc: remove interim ... error which rejects valid code.

It's been six months.

R=rsc
CC=golang-dev
https://golang.org/cl/4289073

src/cmd/gc/typecheck.c

@@ -1634,11 +1634,6 @@ typecheckaste(int op, Node *call, int isddd, Type *tstruct, NodeList *nl, char *
 	for(tl=tstruct->type; tl; tl=tl->down) {
 		t = tl->type;
 		if(tl->isddd) {
-			if(nl != nil && nl->n->op == ONAME && nl->n->isddd && !isddd) {
-				// TODO(rsc): This is not actually illegal, but it will help catch bugs.
-				yyerror("to pass '%#N' as ...%T, use '%#N...'", nl->n, t->type, nl->n);
-				isddd = 1;
-			}
 			if(isddd) {
 				if(nl == nil)
 					goto notenough;

test/fixedbugs/bug252.go

@@ -7,9 +7,9 @@
 package main
 
 func f(args ...int) {
-	g(args)	// ERROR "[.][.][.]"
+	g(args)
 }
 
 func g(args ...interface{}) {
-	f(args)	// ERROR "[.][.][.]"
+	f(args)	// ERROR "cannot use|incompatible"
 }