refactor(runtime): remove Agent class, absorb into BuiltInAgent

Author: AlemTuzlak

packages/runtime/src/agent/agent.ts

@@ -1611,5 +1611,4 @@ export class BasicAgent extends BuiltInAgent {
 /** @deprecated Use BuiltInAgentClassicConfig instead */
 export type BasicAgentConfiguration = BuiltInAgentClassicConfig;
 
-export { Agent, type AgentConfig, type AISDKAgentConfig, type TanStackAgentConfig, type CustomAgentConfig } from "./agent";
 export * from "./converters";