-[FlutterViewControllerTest testkeyboardWillChangeFrameWillStartKeyboardAnimation] was failing when -[FlutterTextInputPluginTest testInputViewsHasNonNilInputDelegate] was run first. The latter test was adding a FlutterTextInputView to the app, testing it, but not removing it when it was complete. Remove it from the view hierarchy at the end of the test.

I still need to investigate why this test was passing on iOS 15 but fails on iOS 16.

Fixes flutter/flutter#109655

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