Remove tmux config

[marksteward]

I don't think any of these tmux tweaks are needed, and have added an init command of echo > /root/.tmux.conf to reset them.

But this is confusing for others and I think it should be the other way around - you should add your own init commmand to create this config if that's what you want.

Or perhaps there should be a way to upload custom files that will get copied into the filesystem, or a way to select a different docker image to run?