Move getMobileProvisioningUrl parsing to telephony

ConnectivityService is going to become mainline and can not
access hidden APIs. Telephony and Settings were both accessing
the hidden API ConnectivityManager#getMobileProvisioningUrl.
Moving #getMobileProvisioningUrl method into telephony means
that there is one less access to a hidden API within the overall
framework since the Connectivity stack never needed this value.
Thus, move getMobileProvisioningUrl parsing to telephony surface
from ConnectivitySerivce and replace the corresponding access in
DcTracker.

Bug: 175177794
Test: atest FrameworksTelepohonyTests
Test: verify that the url could be read from both resource and file
Change-Id: Icb451ecd2cff9205bf3ffb3636e5ef93cba53a43