Fix issue #35309312: Background start not allowed: service...

...Intent { flg=0x100 cmp=com.android.systemui/.SystemUIService }
to com.android.systemui/.SystemUIService from pid=28245 uid=1000 pkg=android

Rework the persistent app check to just directly look at the package
manager (but as efficiently as possible).  My idea for trying to keep
this in the UidRecord was stupid. :p

Test: manually tested it boots
Change-Id: I5a88717a27fa3529048d37a853518a3ec04055db