C#: Fix editor integration breaking and causing error spam when reloading assemblies fails

- Do not reload scripts from non-collectible assemblies
- Do not load GodotTools as collectible
- Do not attempt to reload the same project assembly forever

modules/mono/csharp_script.h

@@ -347,7 +347,6 @@ class CSharpLanguage : public ScriptLanguage {
 	String _debug_error;
 
 	friend class GDMono;
-	void _on_scripts_domain_about_to_unload();
 
 #ifdef TOOLS_ENABLED
 	EditorPlugin *godotsharp_editor = nullptr;