ModuleRegistry: Delete Module after all are stopped

If a Module is stopped, it may still receive callback from lower level
Module, because the callback may have already been in lower level
Module's Handler queue. Instead of deleting the stopped Module
immediately, wait until all Modules are stopped.

Bug: 150174451
Test: bluetooth_test_gd
Change-Id: I0b55fe0ac7da09332d381d2192235339a9dc23fa