[ruby/reline] Remove not implemented method

(ruby/reline#680)

ruby/reline@84762fc588

Author: ima1zumi

lib/reline/key_actor/emacs.rb

@@ -55,7 +55,7 @@ class Reline::KeyActor::Emacs < Reline::KeyActor::Base
     #  26 ^Z
     :ed_ignore,
     #  27 ^[
-    :em_meta_next,
+    :ed_unassigned,
     #  28 ^\
     :ed_ignore,
     #  29 ^]

lib/reline/line_editor.rb

@@ -2630,7 +2630,4 @@ def finish
     @mark_pointer = new_pointer
   end
   alias_method :exchange_point_and_mark, :em_exchange_mark
-
-  private def em_meta_next(key)
-  end
 end