; Revert "Ensure undo-boundary after insert-file-contents."

This reverts commit 6cdd8f71.

The original commit did not address the problem it was claiming to.

src/fileio.c

@@ -4047,14 +4047,8 @@ by calling `format-decode', which see.  */)
 	 being called in insert_from_buffer (via in
 	 prepare_to_modify_buffer).  */
       specbind (intern ("buffer-file-name"), Qnil);
-
-      /* Temporarily enable the undo-buffer to ensure that the change
-         is marked as an undoable one. Bug #23785. */
-      bset_undo_list(current_buffer,Qnil);
       insert_from_buffer (XBUFFER (conversion_buffer),
 			  same_at_start_charpos, inserted_chars, 0);
-      bset_undo_list(current_buffer,Qt);
-
       /* Set `inserted' to the number of inserted characters.  */
       inserted = PT - temp;
       /* Set point before the inserted characters.  */