Remove ACTION_BOOT_COMPLETED filters

Only SystemUIApplication will listen for ACTION_BOOT_COMPLETED with
SYSTEM_HIGH_PRIORITY. SystemUI subclasses will get onBootCompleted
directly whereas other classes can get it through BootCompleteCache.
Therefore classes need not wait for a call that may never happen.

Also, removed onBootComplete from KUM as it was not being used (and
there's a separate cache now).

Finally, fix BroadcastDispatcher to also reject IntentFilter with set
priority != 0.

Test: atest BroadcastDispatcher
Test: build and log that onBootComplete related calls are happening
Change-Id: I0dff299c715cea3228a944aac9ad57bb4ae71339