fix(vertico): backspace keybind for tty users

The input event, [backspace], is only emitted in GUI Emacs, not TTY
Emacs.

Ref: https://discourse.doomemacs.org/t/2491/3

Author: hlissner

modules/completion/vertico/config.el

@@ -29,7 +29,7 @@ overrides `completion-styles' during company completion sessions.")
   ;; cleans ~/foo/bar/// to /, and ~/foo/bar/~/ to ~/.
   (add-hook 'rfn-eshadow-update-overlay-hook #'vertico-directory-tidy)
   (add-hook 'minibuffer-setup-hook #'vertico-repeat-save)
-  (map! :map vertico-map [backspace] #'vertico-directory-delete-char))
+  (map! :map vertico-map "DEL" #'vertico-directory-delete-char))
 
 
 (use-package! orderless