Per the comment at top, this test is about whether the GC runs during
init, but it was testing more than that, and testing how much the GC
collected in a certain amount of time.

Instead, loosen this test to just see whether it ran at all and not
how well it did.

Fixes #9848

Change-Id: I31da7dd769140d7b49aa6c149a543fae6076aa5e
Reviewed-on: https://go-review.googlesource.com/4820Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>