Allows properly keyed radios to broadcast in robot talk and/or hivemind + some cleanup

This was originally meant to be included in Zuhayr's xenorewrite and *was* merged into the PR, but while looking through radio code I noticed it wasn't present on master (I guess it got lost when he closed and reopened his PRs?).

This is targeted to master since it was going to be included in the last merge, however it can be switched to dev if that is preferred.

Original PR description:
> * Allows properly keyed radios to broadcast in robot talk and/or hivemind
* Fixes encryption key w_class
* Cleans up used_radio handling in saycode
* Removes unused devices/radio code

This block of code here is the main change to the talk_into() proc. The code between the comment "/#### Grab the connection datum ####//" and the check for istype(connection) was moved into the handle_message_mode() proc, which makes the radio do things based on the message mode (mainly it selects the channel to send messages on).

Everything else in this file is due to changing indentation.