Migrate stray NotificationEntry usages in ENR

Migrate direct usages of mEntry and remove some dead code.

Test: BundleEntryTest
Test: NotificationEntryTest
Test: OriginalUnseenKeyguardCoordinatorTest
Test: ExpandableNotificationRowTest
Test: NotificationGutsManagerWithScenesTest
Test: NotificationMenuRowTest
Bug: 395857098
Flag: com.android.systemui.notification_bundle_ui
Change-Id: I73fe0893823a6f7c717422334fadc91285b18f74