rcutorture: Dispense with Dracut for initrd creation

The dracut scripting does not work on all platforms, and there are no
known failures from the init binary based on the statically linked C
program.  This commit therefore removes the dracut scripting so that the
statically linked C program is always used to create the init "script".

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>