Flush all received session callback events before attempting tear down

Some tests accumulate a lot of unhandled RangingEvents,
this is causing timeouts when attempting to deinit the session:
the tester spends too much time unqueuing them and timeouts before
getting the Closed event

Bug: 333463192
Test: atest CtsUwbMultiDeviceTestCase_FiraRangingTests:RangingTest#test_ranging_nearby_share_profile_bg_fails
Test: atest CtsUwbMultiDeviceTestCase_FiraRangingTests:RangingTest#test_ranging_nearby_share_profile_verify_app_in_bg_stops_session
Change-Id: I88dac5e1c77f7a56b67126faf85da8f8ec23d9c1
diff --git a/tests/cts/hostsidetests/multidevices/uwb/lib/uwb_ranging_decorator.py b/tests/cts/hostsidetests/multidevices/uwb/lib/uwb_ranging_decorator.py
index c306291..d20eed3 100644
--- a/tests/cts/hostsidetests/multidevices/uwb/lib/uwb_ranging_decorator.py
+++ b/tests/cts/hostsidetests/multidevices/uwb/lib/uwb_ranging_decorator.py
@@ -270,6 +270,7 @@
     Args:
     """
     for session in self._callback_keys:
+      self.clear_ranging_session_callback_events(session)
       self.ad.uwb.closeRangingSession(self._callback_keys[session])
       self.verify_callback_received("Closed", session)
     self.clear_all_ranging_sessions()