vim:keys: Map real <C-BS> to delete one word

Map <C-BS> (i.e. Ctrl-Backspace) to delete one word in insert mode & co.
as it is properly recognized in some terminals implementing [fixterm][1]
(e.g. kitty and patched st).

Keep the <C-H> mapping for other terminals but reuse the <C-BS> mapping.

[1]: http://www.leonerd.org.uk/hacks/fixterms/

.config/vim/vimrc.d/40-keys.vim

@@ -33,7 +33,8 @@ if (has('clipboard'))
 endif
 
 " Ctrl-Backspace should delete words in insert mode and on command-line.
-noremap! <C-H> <C-W>
+noremap! <C-BS> <C-W>
+map! <C-H> <C-BS>
 
 " Correct word with best/first suggestion.
 noremap <leader>c 1z=