Remove observer specific logic in PackageWatchdog

PackageWatchdog should not directly call RescueParty APIs.
Moving isRecoveryTriggeredReboot API to PackageWatchdog, as it can
return true even if RollbackPackageHealthObserver triggers reboot.

Bug: 289203818
Test: TH
Flag: android.crashrecovery.flags.synchronous_reboot_in_rescue_party
Change-Id: I26efd6731bad1419ccdbeba461b64c36b054425e