chore: remove mcp impl from demo

demo/nextjs/app/.well-known/oauth-authorization-server/route.ts

@@ -1,4 +0,0 @@
-import { oAuthDiscoveryMetadata } from "better-auth/plugins";
-import { auth } from "../../../lib/auth";
-
-export const GET = oAuthDiscoveryMetadata(auth);

demo/nextjs/app/api/[transport]/route.ts

@@ -1,38 +0,0 @@
-import { createMcpHandler } from "@vercel/mcp-adapter";
-import { withMcpAuth } from "better-auth/plugins";
-import { z } from "zod";
-import { auth } from "@/lib/auth";
-
-const handler = withMcpAuth(auth, (req, session) => {
-	return createMcpHandler(
-		(server) => {
-			server.tool(
-				"echo",
-				"Echo a message",
-				{ message: z.string() },
-				async ({ message }) => {
-					return {
-						content: [{ type: "text", text: `Tool echo: ${message}` }],
-					};
-				},
-			);
-		},
-		{
-			capabilities: {
-				tools: {
-					echo: {
-						description: "Echo a message",
-					},
-				},
-			},
-		},
-		{
-			redisUrl: process.env.REDIS_URL,
-			basePath: "/api",
-			verboseLogs: true,
-			maxDuration: 60,
-		},
-	)(req);
-});
-
-export { handler as GET, handler as POST, handler as DELETE };