Resolve flaky audio routing CUJ tests

Cleans up the flaky audio routing tests which were verifying endpoints
switches. It turned out that the test were flaky from other tests not
properly cleaning up. The audio focus was not being abandoned and the
routing hadn't been processed up to that point. This ended up leaking
into subsequent tests where audio routing requests were piling up from
multiple tests. Asserting MODE_NORMAL here isn't sufficient as it
doesn't account for the audio routing to have been processed so waiting
to process the tests with SystemClock.sleep is sufficient enough to give
the routing enough time to finish processing the end of the call.

Bug: 384101577
Test: atest CtsTelecomCujTestCases:SingleCallingTest
Flag: EXEMPT test fix
Change-Id: Iaa5b203b7d1d71fcd7fded2434f34e60566d882e