osmo-bts-trx: vty: clarify and improve some deprecation messages
osmo-bts-trx: vty: clarify and improve some deprecation messages

Change-Id: I22b69eccfa50d178bd36bf770f7158ec441c9923
Related: SYS#4918

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts