For deleting a word while in the shell, I find it easier/faster to use
emacs bindings or Ctrl-Backspace and backward-kill-word instead of the
vi version.
In tmux, Ctrl-H (same esacape sequnce as Ctrl-Backspace) is used for
switching panes since f11b7fa56545 ("vim,tmux:plugs: Add
`vim-tmux-navigator`"), so I need to use Ctrl-W.
As that is bound to vi-backword-kill-word, rebind it to use the emacs
version.