cmd/compile: temporarily disable Formats test

So we can submit a sequence of older changes that don't yet
update the formats in this file. We will then re-enable the
test with the updated formats.

Change-Id: I6ed559b83adc891bbf4b3d855a7dc1e428366f7f
Reviewed-on: https://go-review.googlesource.com/28776Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/fmt_test.go

@@ -66,6 +66,8 @@ type CallSite struct {
 }
 
 func TestFormats(t *testing.T) {
+	return // temporarily disabled
+
 	testenv.MustHaveGoBuild(t) // more restrictive than necessary, but that's ok
 
 	// determine .go files