time: Fix ordering of slots in AfterQueueing test

We shouldn't sort the slots array, as it is used each time the
test is run.  Tests after the first should continue to use the
unsorted ordering.

Note that this doesn't fix the flaky test.  Just a bug I saw
while investigating.

Change-Id: Ic03cca637829d569d50d3a2278d19410d4dedba9
Reviewed-on: https://go-review.googlesource.com/9637


Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>