Revert bb369334722b23120bf0b0e91e6a6c69e0884474

We aren't sure why this change was made, and reverting it appears to help
fix mouse issues in emacs related to text hilighting.

Signed-off-by: Andrew Chin <achin@eminence32.net>
Implement UTF8 mouse mode (SET_EXT_MODE_MOUSE DECSET 1005)

Signed-off-by: Andrew Chin <achin@eminence32.net>
Clear other mouse modes if 1000 or 1002 are set

I'm not sure if this is correct, but tmux does this!

Signed-off-by: Andrew Chin <achin@eminence32.net>
terminalfunctions.cc: Refactor out set_if_available()