rcutorture: Drop "-soundhw pcspkr" from x86 boot arguments

Because recent testing shows that "-soundhw pcspkr" is no longer required
in the kernel boot arguments, this commit drops this qemu argument.

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>