Get rid of the OverlayEffectsComponent stuff (#3010)

* Get rid of the OverlayEffectsComponent stuff because it just ended up creating workarounds for it's bugs, without removing any functionality

* Flashes and Flashbangs use the same code now (the Flashable path because it's better)

Content.Server/ServerNotifyManager.cs

@@ -1,6 +1,7 @@
 using Content.Server.Administration;
 using Content.Server.Interfaces;
 using Content.Shared;
+using Content.Shared.Network.NetMessages;
 using Content.Shared.Administration;
 using Content.Shared.Interfaces;
 using Robust.Server.Interfaces.Console;