Replace kgm call with local in shouldShowRedacted

There is no need to make a binder call to the KeyguardManager to
determine device locked state for every notification, when we already
have an observed stateflow for the KeyguardInteractor

Bug: 388207862
Test: atest NotificationLockscreenUserManagerTest
Flag: android.app.redact_sensitive_content_notifications_on_lockscreen
Change-Id: I0d822da880a34a18e79e8e9d6d5c26ffe3297210