cmd/pack: simplify the testing logic slightly

Followup to https://go-review.googlesource.com/3910

We only need 1000 iteratinons.

Change-Id: Ib63ae53105176abec77bad9609d638aeda7bcd61
Reviewed-on: https://go-review.googlesource.com/3901Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/pack/pack_test.go

@@ -257,15 +257,8 @@ func TestLargeDefs(t *testing.T) {
 		}
 	}
 
-	n := 10000
-	if testing.Short() {
-		// Issue 9656: 10,000 is too aggressive for several
-		// builders, with ~120 MB of disk consumed. 1,000 is
-		// still enough to exercise the old bug.
-		n = 1000
-	}
 	printf("package large\n\ntype T struct {\n")
-	for i := 0; i < n; i++ {
+	for i := 0; i < 1000; i++ {
 		printf("f%d int `tag:\"", i)
 		for j := 0; j < 100; j++ {
 			printf("t%d=%d,", j, j)