test: disable flaky heapsampling test for now

Flaky tests do more harm than good.

Updates #13098

Change-Id: I179ed810b49bbb96c8df462bfa20b70231b26772
Reviewed-on: https://go-review.googlesource.com/16521
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/heapsampling.go

@@ -25,6 +25,8 @@ var a64k *[64 * 1024]byte
 // vary for run to run. This test only checks that the resulting
 // values appear reasonable.
 func main() {
+	return // TODO: fix this flaky test; golang.org/issue/13098
+
 	const countInterleaved = 10000
 	allocInterleaved(countInterleaved)
 	checkAllocations(getMemProfileRecords(), "main.allocInterleaved", countInterleaved, []int64{256 * 1024, 1024, 256 * 1024, 512, 256 * 1024, 256})