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/ClusterFlashComponent.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
+using Content.Server.Explosion.EntitySystems;
 using Content.Server.Flash.Components;
 using Content.Server.Throwing;
 using Content.Shared.Explosion;