ui: Remove use of defunct haunt-error.

* haunt/ui.scm (run-haunt-command): Remove call to 'haunt-error'.

haunt/ui.scm

@@ -116,7 +116,7 @@ There is NO WARRANTY, to the extent permitted by law.~%"
             (lambda ()
               (resolve-interface `(haunt ui ,command)))
             (lambda -
-              (haunt-error "~a: command not found" command)
+              (format (current-error-port) "~a: invalid subcommand~%" command)
               (show-haunt-usage))))
          (command-main (module-ref module (symbol-append 'haunt- command))))
     (parameterize ((program-name command))