chore(typescript): fixes dart failures and linter

Closes #4359

modules/angular2/src/http/http.ts

@@ -20,10 +20,7 @@ function mergeOptions(defaultOpts, providedOpts, method, url): RequestOptions {
       url: providedOpts.url,
       search: providedOpts.search,
       headers: providedOpts.headers,
-      body: providedOpts.body,
-      mode: providedOpts.mode,
-      credentials: providedOpts.credentials,
-      cache: providedOpts.cache
+      body: providedOpts.body
     }));
   }
   if (isPresent(method)) {

modules/angular2/src/http/interfaces.ts

@@ -40,9 +40,6 @@ export type RequestOptionsArgs = {
   headers?: Headers;
   // TODO: Support Blob, ArrayBuffer, JSON, URLSearchParams, FormData
   body?: string;
-  mode?: any;
-  credentials?: any;
-  cache?: any;
 }
 
 /**