Fixing flakey tests

Sometimes if the system is slow or the process isn't scheduled in time,
our test may take a long time. We still want to test the async
flow, and exclude the flakyness in the rest of the cases, so we
removed the timeout.

Test: runtest systemui
Change-Id: I562d0798d274ca93d9ae0644f44504428d84023c
Fixes: 38184803