rcu: Remove swake_up_one_online() bandaid

It's now ok to perform a wake-up from an offline CPU because the
resulting armed scheduler bandwidth hrtimers are now correctly targeted
by hrtimer infrastructure.

Remove the obsolete hackerry.

Link: https://lore.kernel.org/all/20241231170712.149394-3-frederic@kernel.org/


Reviewed-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>