CST: remove AT%Nxxxx old AEC control This crude method of enabling and configuring AEC is not compatible with L1_NEW_AEC, and even for the old AEC it did not support every possible combination. It is time for this hack to go. The new and proper way of enabling and configuring AEC is via RiViera Audio Service audio mode facility, either audio mode files or full access write, most directly accessible via fc-tmsh auw 12 for free experimentation.