emacs: always run gofmt on code at save time

Signed-off-by: Ben Walton <bdwalton@gmail.com>
emacs: drop duplicate activation of midnight-mode

Signed-off-by: Ben Walton <bdwalton@gmail.com>
emacs: set default tab width of 2

Signed-off-by: Ben Walton <bdwalton@gmail.com>
tmux: drop some keybindings that I never use

Signed-off-by: Ben Walton <bdwalton@gmail.com>