Update screenshot action system window dismiss fix

Switches the flag to a bugfix flag.

The keyguard dismissal change was unrelated and is now
moved out of the flag check since the behavior is unaffected
by the flag value with duplicated code removed.

Bug: 309933761
Test: ActionIntentExecutorTest
Flag: com.android.systemui.fix_screenshot_action_dismiss_system_windows
Change-Id: I1f20437aacf7fc55e53ff08090d1c4e38dc085fc