Change VmProviderSettingsUtil methods to static.

I plan to create a VoicemailProviderListPreference, and move the
initVoicemailProviders code into the preference. In context of this,
the current instance-based implementation of the settings util
seems to be less flexible; a context can simply be passed in to
obtain the SharedPreferences object as necessary.

Bug: 18232725
Change-Id: Ie9a46925a2e5fbb1bf89dcc58ca5bf2e18496513
2 files changed