Clean new TelephonyManager API.

This is to apply API council's review opinion on a previous commit.

We are reverting previous change, which renamed isDataEnabled and
setDataEnabled to isUserMobileDataEnabled and setUserMobileDataEnabled.
So this commit will remove the new APIs isUserMobileDataEnabled and
setUserMobileDataEnabled, and also rename hidden API isMobileDataEnabled
to isDataCapable.

Bug: 71584593
Test: unittest
Change-Id: I84d65776874e7a7f6e3a9af9ff7ec7dcbd715c2c