subscription: remove dangling old implementation

Missed this before the commit train left the station.

src/subscription.zig

@@ -41,44 +41,3 @@ pub const Subscription = opaque {
         nats_c.natsSubscription_Destroy(@ptrCast(self));
     }
 };
-
-// pub fn Subscription(T: type) type {
-//     return struct {
-//         const Self = @This();
-
-//         _internal: *nats_c.natsSubscription,
-//         userdata: T,
-//         function: MessageCallback(T),
-
-//         pub fn create(
-//             allocator: std.mem.Allocator,
-//             userdata: T,
-//             callback: MessageCallback(T),
-//         ) AllocError!*Self {
-//             const self: *Self = try std.mem.Allocator.create(Self);
-//             self.userdata = userdata;
-//             self.function = callback;
-//             return self;
-//         }
-
-//         pub fn wrap(
-//             self: *Self,
-//             internal: *nats_c.natsSubscription,
-//         ) void {
-//             // self._internal =
-//         }
-
-//         fn thunk(
-//             conn: ?*nats_c.natsConnection,
-//             sub: ?*nats_c.natsSubscription,
-//             msg: ?*nats_c.natsMsg,
-//             userdata: ?*const anyopaque,
-//         ) callconv(.C) void {
-//             self.function(self.userdata, connection, subscription, message);
-//         }
-//     };
-// }
-
-pub fn MessageCallback(comptime T: type) type {
-    return *const fn (userdata: T, connection: *Connection, subscription: *Subscription, message: *Message) void;
-}