transcoding: remove "not yet implemented" from MNCC manual once transcoding is in place
in osmo-gsm-manuals.git added by change-id Ic71a83d71f2da87e1066fcc060b2b942643eddbc there is a hint that transcoding is not yet implemented by OsmoMGW.
Remove this and double-check that that section describes the situation accurately.
For the new OsmoMSC, the MNCC_BRIDGE command will instruct the separate OsmoMGW to bridge calls, which will be able to handle transcoding between different TCH as well as 3G (IuUP) payloads (but note: not yet implemented at the time of writing this). Hence an external MNCC may decide to bridge calls directly between BTSs or RNCs that both are internal to the OsmoMSC, for optimization reasons.