Dismiss app warning dialogues by CLOSE_SYSTEM_DIALOGS

ActivityManagerTestBase#launchHomeActivityNoWait is called in setUp
and it also sends CLOSE_SYSTEM_DIALOGS.

So these warning dialogues won't affect other tests which rely on
window focus.

Bug: 112837428
Bug: 242608650
Test: atest DeprecatedTargetSdkTest DisplaySizeTest

Change-Id: I651871be836c9fe43874cca326c7041f199f54c0