Allow default dialer changes and phone account enable/disable via ADB

Add commands accessible via adb shell that can be used for CTS tests
without the need for adb root
*set-phone-account-enabled
*set-phone-account-disabled
*set-default-dialer
*get-default-dialer

Modify enablePhoneAccount/setDefaultDialer to indicate success.

Remove now unused functionality in ProtectedEnableAccountPreferenceActivity
and ProtectedChangeDefaultDialerActivity.

Bug: 21583012
Change-Id: I542d145cc969334c004b8344fbbb01f278256f9d