Fix PackageManagerService WTF in systemReady()

This resolves the following error:
F/SystemServer(31979): BOOT FAILURE making Package Manager Service ready
F/SystemServer(31979): java.lang.SecurityException: Unable to find app for caller android.app.ActivityThread$ApplicationThread@42171630 (pid=31979) when registering receiver android.app.LoadedApk$ReceiverDispatcher$InnerReceiver@420d1130
F/SystemServer(31979):  at com.android.server.am.ActivityManagerService.registerReceiver(ActivityManagerService.java:13157)
F/SystemServer(31979):  at android.app.ContextImpl.registerReceiverInternal(ContextImpl.java:1506)
F/SystemServer(31979):  at android.app.ContextImpl.registerReceiverAsUser(ContextImpl.java:1481)
F/SystemServer(31979):  at com.android.internal.content.PackageMonitor.register(PackageMonitor.java:84)
F/SystemServer(31979):  at com.android.server.pm.UserManagerService.systemReady(UserManagerService.java:237)
F/SystemServer(31979):  at com.android.server.pm.PackageManagerService.systemReady(PackageManagerService.java:11305)
F/SystemServer(31979):  at com.android.server.ServerThread.initAndLoop(SystemServer.java:1022)
F/SystemServer(31979):  at com.android.server.SystemServer.main(SystemServer.java:1372)
F/SystemServer(31979):  at java.lang.reflect.Method.invokeNative(Native Method)
F/SystemServer(31979):  at java.lang.reflect.Method.invoke(Method.java:515)
F/SystemServer(31979):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
F/SystemServer(31979):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
F/SystemServer(31979):  at dalvik.system.NativeStart.main(Native Method)

TODO: Revisit this in the future when Google updates AOSP for multiple
system contexts.

Change-Id: I74be7a7a3ba1ede55a8ccae7c86e7650b27f435e