testing: remove tests from the running log while they are waiting on parallel subtests

testing: remove tests from the running log while they are waiting on parallel subtests

The parallel subtests are themselves removed from the running map
while they are blocked on calls to t.Parallel, so it is misleading to
log their parents as if they are running when we know they cannot be
making any kind of meaningful progress.

Fixes #64404.

Change-Id: Iaad11d5d4f4c86d775d36e5285c49629dccddd74
Reviewed-on: https://go-review.googlesource.com/c/go/+/546018
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>