Early checks to avoid unneeded binder calls

We check in NMS also, in case some talks to INotificationManager,
but we should bail in the client process if we can, because there are
many apps that frequently try to delete any notificationchannel that
doesn't match their current desired set

Test: NotificationAssistantServiceTest
Flag: android.service.notification.notification_classification
Fixes: 362327403
Change-Id: Ie118e478b4dc0b2b8ac91fdabd3fccda67c3366a