Remove old todo comment

Author: daymxn

FirebaseAI/Sources/Types/Internal/Live/BidiGenerateContentServerMessage.swift

@@ -17,8 +17,6 @@ import Foundation
 /// Response message for BidiGenerateContent RPC call.
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 struct BidiGenerateContentServerMessage: Sendable {
-  // TODO: Make this type `internal`
-
   /// The type of the message.
   enum MessageType: Sendable {
     /// Sent in response to a `BidiGenerateContentSetup` message from the client.