chore(lint): remove unused imports (#11923)

This was done automatically by tslint, which can now fix issues it finds.
The fixer is still pending in PR https://github.com/palantir/tslint/pull/1568
Also I have a local bugfix for https://github.com/palantir/tslint/issues/1569
which causes too many imports to be deleted.

modules/@angular/http/src/http.ts

@@ -16,7 +16,6 @@ import {RequestMethod} from './enums';
 import {ConnectionBackend, RequestOptionsArgs} from './interfaces';
 import {Request} from './static_request';
 import {Response} from './static_response';
-import {URLSearchParams} from './url_search_params';
 
 function httpRequest(backend: ConnectionBackend, request: Request): Observable<Response> {
   return backend.createConnection(request).response;