rcutorture: Eliminate --rcu-kvm argument

The --rcu-kvm argument was intended to allow the scripts to live in
an alternate location.  Unfortunately, this prevents the kvm.sh script
from using common functions until after it finished parsing arguments,
because it doesn't know where to find them until then.  However, "cp -a"
and "ln -s" work pretty well, so lack of an --rcu-kvm argument can be
easily worked around.

This commit therefore removes this argument.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Greg KH <gregkh@linuxfoundation.org>