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.
CraftBukkit removed their implementation that caused this issue,
switching to Mojang's implementation which doesn't appear to share it. I
already removed the important bit in the last upstream merge, this is
just unused and unnecessary now. So we remove it.
