feat: remove protocol rest json class (#438)

* feat: remove rest-json protocol class

* feat: rename handler to RequestHandler; Consolidate types

Author: AllanZhengYP

packages/protocol-http/src/httpHandler.ts

@@ -1,8 +1,8 @@
 import { HttpRequest } from "./httpRequest";
 import { HttpResponse } from "./httpResponse";
-import { TransferHandler, HttpOptions } from "@aws-sdk/types";
+import { RequestHandler, HttpOptions } from "@aws-sdk/types";
 
-export type HttpHandler = TransferHandler<
+export type HttpHandler = RequestHandler<
   HttpRequest,
   HttpResponse,
   HttpOptions