Remove most IEntity usages from explosions (#5240)

* Remove most IEntity usages from Destructible and Explosions

* Perform a minute amount of cleanup

* Fix build

Content.Server/Explosion/Components/OnUseTimerTriggerComponent.cs

@@ -1,4 +1,5 @@
 using System;
+using Content.Server.Explosion.EntitySystems;
 using Content.Shared.Interaction;
 using Content.Shared.Trigger;
 using Robust.Server.GameObjects;