Use em_delete in key_delete

When the editing mode is emacs, use `em_delete` in `key_delete`. We need
to add a condition though to `em_delete`, because it implements both
`delete-char` and `end-of-file`. We only want the `end-of-file` behavior
is the key is really Ctrl-D.

lib/reline/line_editor.rb

@@ -1957,8 +1957,10 @@ def finish
   end
 
   private def key_delete(key)
-    if @config.editing_mode_is?(:vi_insert, :emacs)
+    if @config.editing_mode_is?(:vi_insert)
       ed_delete_next_char(key)
+    elsif @config.editing_mode_is?(:emacs)
+      em_delete(key)
     end
   end
 
@@ -2664,7 +2666,7 @@ def finish
   alias_method :kill_whole_line, :em_kill_line
 
   private def em_delete(key)
-    if @line.empty? and (not @is_multiline or @buffer_of_lines.size == 1)
+    if @line.empty? and (not @is_multiline or @buffer_of_lines.size == 1) and key == 4
       @line = nil
       if @buffer_of_lines.size > 1
         scroll_down(@highest_in_all - @first_line_started_from)