librem5.pa: Disable unwanted audio processing in echo cancelation module

module-echo-cancel uses WebRTC AEC algorithm to filter out acoustic echo. It's mostly meant for desktop use with speakers and microphone, therefore by default it does additional processing for things like voice detection or noise suppression in order to filter out things like keyboard typing. However, it appears that at times this filter may be a bit too overzealous for our mobile phone use case, with users reporting the voice coming out on the other side as "muffled".

Since echo cancellation is all that we cared about when enabling the filtering, let's disable any kind of processing that's not related to removing the echo to make sure it doesn't have any unintended consequences. In the end nothing prevents us from selectively reenabling particular features after enough testing.

Note: module-echo-cancel also supports AECM (mobile) variant of the algorithm that theoretically should better match our use case. However, so far I wasn't able to make it work (my current suspicion is that we have to reduce the overall latency in order for it to actually filter out the echo).