How to remove output from inherited package?

[Bodertz]

In trying to create a transmission-qt package, I inherit from
transmission, remove the gtkmm dependency and the phases that deal with
moving transmission-gtk to the :gui output, and add a few qt
dependencies so that transmission-qt is built.  See the package
definition below:

    (define-module (bodertz transmission-qt)
      #:use-module (gnu packages bittorrent)
      #:use-module (gnu packages qt)
      #:use-module (guix packages)
      #:use-module (guix gexp)
      #:use-module (guix utils))

    (define-public transmission-qt
      (package
        (inherit transmission)
        ;; (outputs '("out"))
        (name "transmission-qt")
        (arguments
         (substitute-keyword-arguments (package-arguments transmission)
           ((#:phases phases)
            #~(modify-phases #$phases
                (delete 'move-gui)
                (delete 'glib-or-gtk-wrap)
                (delete 'wrap-program)))))
        (inputs (modify-inputs (package-inputs transmission)
                  (delete "gtkmm")
                  (append qtbase qttools qtsvg)))))

This works fine, except that an unnecessary transmission-qt:gui output
is created which contains license files (apologies if the email messes
up the formatting):

    $ tree /gnu/store/k34zx89kvd712maqfi62spnbb5s31bqd-transmission-qt-4.0.6-gui
    /gnu/store/k34zx89kvd712maqfi62spnbb5s31bqd-transmission-qt-4.0.6-gui
    └── share
        └── doc
            └── transmission-qt-4.0.6
                ├── bsd-3-clause.txt
                ├── COPYING
                ├── gpl-2.0.txt
                ├── gpl-3.0.txt
                └── mit.txt


When I uncomment the ;; outputs '("out")) line from my package
definition, I expected that it would only create the ordinary :out
output, but instead, I get this error:

    $ guix build transmission-qt
    [...]
    builder for 
`/gnu/store/026fwjchyis1x99iqsgliqga284wydbc-transmission-qt-4.0.6.drv' failed 
to produce output path 
`/gnu/store/v331nyi7kqg4gi432gvhz1c719n8x7xf-transmission-qt-4.0.6-gui'


Is there a way to avoid the attempt to create a :gui output?