Changes

mgw: osmo-mgw.cfg: remove deprecated no-op params

This patch fixes the following warnings:

% Deprecated 'sdp audio-payload number <0-255>' config no longer has any effect
% Deprecated 'sdp audio-payload name NAME' config no longer has any effect
% Deprecated 'loop (0|1)' config no longer has any effect
% Deprecated 'allow-transcoding' config no longer has any effect
% Deprecated 'loop (0|1)' config no longer has any effect
% Deprecated 'allow-transcoding' config no longer has any effect

Change-Id: Ie4f2b46eda2e848781b77e590ad20e80fed86257