Kill uid when REQUEST_INSTALL_PACKAGES is denied

Process privileges like open fds need to be revoked, when this
permission is denied by the user.

Test: Manually verified by checking logs.
Robotest:
atest SettingsRoboTests:ExternalSourcesDetailsTest

Bug: 133504844
Change-Id: I81da0b3a5d6c54e392828829d1a2c43488439504