rcutorture/kvm.sh: Remove unused variable, `alldone`

The variable `alldone` is defined but not used within an awk script.
This commit therefore removes it.

Fixes:53954671 ("rcutorture: Do better bin packing")

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>