Revert "qemu: Use heads parameter for QXL driver"
    
    This reverts commit 7b401c3bdacdf8367a0070e625d73eafb802045d.
    
    Until libvirt is able to differentiate whether heads='1' is just a
    leftover from previous libvirt or whether that's added by user on
    purpose and also whether the domain was started with the support for
    qxl's max_outputs, we cannot incorporate this patch into the tree
    due to compatibility reasons.
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>