docs: timers: drop documentation about LB_BIAS

The LB_BIAS feature was removed in commit 1c1b8a7b ("sched/fair:
Replace source_load() & target_load() with weighted_cpuload()"), so drop
the mention that it is disabled in the no_hz case.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

Link: https://lore.kernel.org/r/1595088518-28116-1-git-send-email-Julia.Lawall@inria.fr


Signed-off-by: Jonathan Corbet <corbet@lwn.net>