IListener and IRadio purge (#11980)

Content.Server/Radio/Components/ActiveRadioComponent.cs

@@ -0,0 +1,17 @@
+using Content.Shared.Radio;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype.Set;
+
+namespace Content.Server.Radio.Components;
+
+/// <summary>
+///     This component is required to receive radio message events.
+/// </summary>
+[RegisterComponent]
+public sealed class ActiveRadioComponent : Component
+{
+    /// <summary>
+    ///     The channels that this radio is listening on.
+    /// </summary>
+    [DataField("channels", customTypeSerializer: typeof(PrototypeIdHashSetSerializer<RadioChannelPrototype>))]
+    public HashSet<string> Channels = new();
+}