Remove ability to enable/disable phoneaccounts (2/6)

Enabling/disabling of phone accounts was only used for SIP accounts and
is no longer necessary for the purpose it was put in.
- Remove all references to enabling/disabling phone accounts
- Remove PhoneAccountSelectionPreferenceActivity and related UI code
+ Rename getEnabledPhoneAccounts -> getCallCapablePhoneAccounts

Bug: 17510811

Change-Id: I6ea5c73bc62f35c2e487dd4d1262c0336b8b6e1e
10 files changed