Printing command ACKs is way too verbose.

A console message is printed every time MAVProxy receives a command ACK message; this disrupts being able to use the CLI. For instance, if the aircraft has a MAVLink gimbal, then commands from the flight controller to the gimbal get ACK'd at something like 50Hz; this renders the MAVProxy CLI into a useless wall of scrolling text.

Better options could be:
- Detecting and suppressing large numbers of duplicate ACKs.
- Only printing ACKs which were specifically expected in response to a command sent by MAVProxy.
- Terminal manipulation so that the incoming messages are printed on a single line of the console, rather than causing the entire CLI to scroll.
- Just not printing them at all.

Start by tracing where MAVProxy receives and prints MAVLink command ACK messages in the CLI, then reproduce the high-rate ACK stream described with a MAVLink gimbal. Done means routine ACK traffic no longer overwhelms the terminal while any necessary command feedback remains usable.

Written by the indexing model from the issue text.