rcutorture: Remove redundant rcutorture_one_extend() from rcu_torture_one_read()

rcutorture: Remove redundant rcutorture_one_extend() from rcu_torture_one_read()

This commit removes a harmless but potentially confusing invocation of
rcutorture_one_extend() within rcu_torture_one_read().  The immediately
preceding call to rcu_torture_one_read_start() already does this cleanup,
and the other call to rcu_torture_one_read_start() already relies on this.

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