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/SoundOnTriggerComponent.cs

@@ -1,3 +1,4 @@
+using Content.Server.Explosion.EntitySystems;
 using Content.Shared.Sound;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Serialization.Manager.Attributes;