Phone number only available if telephony capable

The Phone Number field in either the about or network details pages
should not be shown if the device does not have telephony
capabilities.

Bug: 392808943
Flag: EXEMPT bugfix
Test: atest PhoneNumberPreferenceControllerTest
Test: atest MobileNetworkPhoneNumberPreferenceControllerTest

Change-Id: I04f682cc829d5dc7879e6cdacdaebc55a3b6fd2c