Remove [Signal] attribute from events

- Remove event as a valid target of `SignalAttribute`
- Stop adding the `[Signal]` attribute to events in bindings_generator
- Make bindings_generator use the `EventHandler` suffix to be consistent with the C# source generator
- Remove obsolete comment about the signal's delegate name

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators/ScriptSignalsGenerator.cs

@@ -117,10 +117,6 @@ namespace Godot.SourceGenerators
             source.Append(symbol.NameWithTypeParameters());
             source.Append("\n{\n");
 
-            // TODO:
-            // The delegate name already needs to end with 'Signal' to avoid collision with the event name.
-            // Requiring SignalAttribute is redundant. Should we remove it to make declaration shorter?
-
             var members = symbol.GetMembers();
 
             var signalDelegateSymbols = members