buffer: Remove obsolete actions-on-return.

The assignment of this action is a no-op since the actions for these sources are
re-defined elsewhere.

Also, setting buffer-load as an action-on-return is not valid.  See buffer-load*
for the action that is valid.

source/buffer.lisp

@@ -1465,7 +1465,7 @@ URL-DESIGNATOR is then transformed by BUFFER's `buffer-load-hook'."
                            (history-initial-suggestions)))
    (prompter:enable-marks-p t)
    (prompter:filter-preprocessor nil)   ; Don't remove non-exact results.
-   (prompter:actions-on-return #'buffer-load))
+   )
   (:export-class-name-p t)
   (:metaclass user-class))
 
@@ -1620,8 +1620,7 @@ Finally, if nothing else, set the `engine' to the `default-search-engine'."))
       (declare (ignore suggestions source))
       (input->queries input
                       :check-dns-p t
-                      :engine-completion-p t)))
-   (prompter:actions-on-return #'buffer-load))
+                      :engine-completion-p t))))
   (:export-class-name-p t)
   (:documentation "This prompter source tries to \"do the right thing\" to
 generate a new URL query from user input.