ConnectivityServiceTest: eliminate remaining sleep()

ConnectivityServiceTest was still using sleep() in a few places although
these were unnecessary:
  - in testSatisfiedThenLostNetworkRequestDoesNotTriggerOnAvailable(),
    expectNoCallback() and expectAvailableCallback() already include
    waitForIdleHandler calls that drain the message queues and make
    sleep no-ops.
  - in testTimedoutAfterUnregisterdNetworkRequest, the sleeps were
    introduced before unregisterNetworkCallback was changed to have a
    synchronous effect for callback unregistration, therefore the sleep
    becomes simply non-sensical. To reflect this the name of the method
    is also changed.

Bug: 62918393
Test: runtest frameworks-net
Change-Id: I7b701ecf5846a5e1890e86107b8d2544b419ce44