Remove expecting DOWN events in TAPL tests.

ACTION_UP is always preceded by ACTION_DOWN which means when launcher
receives an UP events, down event is obviously sent.

In b/325377690 , we started seeing only in P9 devices the DOWN events didn't reach TAPL. I added InputDispatcher logs which shows both DOWN and UP events are sent by system_server to NexusLauncher.
However TAPL doesn't receive it. After spending lot of time debugging this, I think we are safe to remove DOWN event expectation in TAPL.

Bug: 325377690
Test: Manual, TAPL presubmits
Flag: NA
Change-Id: I6d3587c488d45e3dc53d2c1c4f3b6b49285eae94