Instead of overriding add within the queue, never add runnables to the
queue if the light queue is disabled.
This change is made to make timings reports and stacktraces less
confusing for administrators, who prior to this change, would have seen
the lighting queue referenced in both, regardless of whether or not it
was enabled.
This change should not affect performance, nor is it made with the
intent to.
Spigot, by default, disables several mechanisms around how chunks are
lit, if ever, which has forced them to always send chunks before vanilla
would consider them ready to send, causing for lots of issues around
lighting glitches.
Shamefully, the amount of work to relight chunks can be detremental
to some servers, meaning that forcibily disabling light updates can
cause major performance issues.
as such, we make a compromise; if this "feature" is disabled, we will
only send chunks which are actually ready to be sent, otherwise, we
will always send chunks.
