Enable SystemUse24HourClockPolicyTest under SingleProcessMash

It passes for me locally. I don't see anything in the test or the
underlying code that depends on the mash mode. I'm not sure why it
was being skipped.

Bug: none
Change-Id: I300bd010ffa68c3cb5c6efec2df316752971084c
Reviewed-on: https://chromium-review.googlesource.com/c/1277954
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599044}
1 file changed