Move unrestricted data summary to DataSaverController

DataSaverController currently used in 2 pages,
- Network & internet > Data Saver
- Apps > Special app access

This helps unify the logic, and instead of showing on "Special app
access", this summary shows on "Unrestricted data" is make more sense.

Bug: 280280596
Test: Manually on above pages
Test: Unit test
Change-Id: Ia151ed8179a250f8f20cc5041f9383fffebdab10