docs/interop/bitmaps: Clean up a reference to qemu-qmp-ref

docs/interop/bitmaps: Clean up a reference to qemu-qmp-ref

docs/interop/bitmaps.rst uses references like

    `qemu-qmp-ref <qemu-qmp-ref.html>`_
    `query-block <qemu-qmp-ref.html#index-query_002dblock>`_

to refer to and into docs/interop/qemu-qmp-ref.rst.

Clean up the former: use :doc:`qemu-qmp-ref`.

I don't know how to clean up the latter.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240120095327.666239-5-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>