rcutorture: TASKS_RCU set directly, so don't explicitly set it

The TASKS01, TASKS02, and TASKS03 rcutorture config fragments currently
set CONFIG_TASKS_RCU.  However, now that the value of this Kconfig
parameter is set via "select" statements, it is no longer necessary to
set it explicitly.  This commit therefore removes it from the Kconfig
fragments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>