Handlers should only be cleared and deleted once

- Removed handler clearance management from ModuleRegistry::StopAll().
- Ensured that handler instance new`ed and deleted in the same scope and file.
- Added a WaitUntilStopped() call after `stack_handler_->Clear()` call.

Test: m com.android.bt
Flag: com.android.bluetooth.flags.same_handler_for_all_modules
Bug: 393449774
Bug: 398195386
Bug: 402005761
Change-Id: Iada1114d547c1bc6394227503083104f8790ce21