To allow unit tests to run without platform certificates, remove
signature permission usage in ConnectivityServiceTest.
This mocks permission checks done in ConnectivityService for which the
test assumed that the permission was held, and mocks calls to
BatteryStatsManager. Calls to ActivityManagerService (through
PendingIntent) are done with shell permissions as the test uses real
PendingIntent mechanics.
Bug: 187935317
Test: atest FrameworksNetTests
Change-Id: If309d653ac2e9bbcf1b94bcee6336367289df359
18a979fa41