torture: Remove duplicated argument -enable-kvm for ppc64

The qemu argument -enable-kvm is duplicated because the qemu_args bash
variable in kvm-test-1-run.sh already provides it.  This commit therefore
removes the ppc64-specific copy in functions.sh.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>