Destroy Save UI when it's hidden without a pending restoration.

This scenario typically happens when the BACK button is tapped after
the SaveUI is restored.

Test: cts-tradefed run commandAndExit cts-dev -m CtsAutoFillServiceTestCases -t android.autofillservice.cts.SimpleSaveActivityTest#testTapLink_launchTrampolineActivityThenTapBackAndStartNewSession
Test: cts-tradefed run commandAndExit cts-dev -m CtsAutoFillServiceTestCases -t android.autofillservice.cts.PreSimpleSaveActivityTest#testTapLink_launchTrampolineActivityThenTapBackAndStartNewSession
Test: cts-tradefed run commandAndExit cts-dev -m CtsAutoFillServiceTestCases
Fixes: 65459113

Change-Id: I07c6d9b6d219889c50caeaff99b883841b87d9cc