[smsservice] Read pending MO SMS in startup

Signed-off-by: Martti Piirainen <martti.piirainen@oss.tieto.com>
[tones] Remove dead code related to tones w/o user connection

oFono and our modem simply don't give such detailed information on the audio path.
[call] Play local alert tone if network certainly does not do it

Use oFono VoiceCallAgent API to get notified when a local alert tone (ringback tone) needs to be played.