Some people could have legitimate use for explosions though. And the same effect can also be achieved with spawnprojectile.
What I recommend:
1) If they're using YOUR bricks, they shouldn't have your trust. If they aren't, clear their bricks.
2) /cancelAllEvents not clear.
3) Also ban them.
4) If you're not hosting a freebuild of any sort, you could set events to be admin only.
$Pref::Server::WrenchEventsAdminOnly = 1;
5) If you still just want the explosion event removed after all that being said:
unregisterOutputEvent("Player","spawnExplosion");
unregisterOutputEvent("fxDTSBrick","spawnExplosion");
Just put those two lines in an add-on.