dashboard: unset known issue for staticlockranking builder
dashboard: unset known issue for staticlockranking builder

CL 207619 has been submitted to master, fixing golang.org/issue/38029.
The linux-amd64-staticlockranking builder has been passing since then.
Unset its known issue so that if there are regressions in the future,
they can be investigated.

For golang/go#38029.
For golang/go#37937.

Change-Id: I0de8e4ac122effee56aac73c741fab41512ff0c2
Reviewed-on: https://go-review.googlesource.com/c/build/+/227544
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dan Scales <7338a4f274e3bf1354488b9d1f344f4c9a69a8fb@google.com>

golang/build,golang/build,golang/build,golang/build