Revert "ConnectivityManager#registerNetworkAgent gains an argument"

Original CL (aosp/2792219) was required by aosp/2792436.
But aosp/2792436 broke the CTS and some change needs to be reverted.
And this revert needs the revert of aosp/2792219.

Reason for revert: revert change in aosp/2792436
Reverted changes: /q/submissionid:2792219-localNetworksCM

Change-Id: Ic81ba232f4143711acf97ac25238e4b63a3f2f08