Really allow for hybrid bindings

The previous solution would not erase the previous bindings if
fish_vi_key_bindings was called with a mode argument. So if the user
switched to vi with a different initial mode, they'd keep their previous
bindings also.

Supersedes e89057b.

doc_src/index.hdr.in

@@ -960,7 +960,7 @@ function hybrid_bindings --description "Vi-style bindings that inherit emacs-sty
     for mode in default insert visual
         fish_default_key_bindings -M $mode
     end
-    fish_vi_key_bindings
+    fish_vi_key_bindings --no-erase
 end
 set -g fish_key_bindings hybrid_bindings
 \endfish