Since commit a7424faf QMP is always used.

Also, commit 932534e8 removed the last use of this apart from:
* parsing/formatting this in the caps cache
* using it as a temporary variable to know when to report an error
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>