chore(imports): don't import ExceptionHandler from facade (#10620)

This lets us skip src/facade/exception* when compiling modules other than core.
It prevents having many conflicting declarations

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

@@ -6,11 +6,13 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {BaseException} from '@angular/core';
+
 import {ListWrapper, Map, MapWrapper, StringMapWrapper, isListLikeIterable, iterateListLike} from '../src/facade/collection';
-import {BaseException} from '../src/facade/exceptions';
 import {isBlank} from '../src/facade/lang';
 
 
+
 /**
  * Polyfill for [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers), as
  * specified in the [Fetch Spec](https://fetch.spec.whatwg.org/#headers-class).

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

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {BaseException} from '../src/facade/exceptions';
+import {BaseException} from '@angular/core';
 import {Json, isString} from '../src/facade/lang';
 
 import {ResponseOptions} from './base_response_options';

modules/@angular/http/testing/mock_backend.ts

@@ -6,19 +6,19 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Injectable} from '@angular/core';
+import {BaseException, Injectable} from '@angular/core';
 import {ReplaySubject} from 'rxjs/ReplaySubject';
 import {Subject} from 'rxjs/Subject';
 import {take} from 'rxjs/operator/take';
 
 import {ReadyState} from '../src/enums';
-import {BaseException} from '../src/facade/exceptions';
 import {isPresent} from '../src/facade/lang';
 import {Connection, ConnectionBackend} from '../src/interfaces';
 import {Request} from '../src/static_request';
 import {Response} from '../src/static_response';
 
 
+
 /**
  *
  * Mock Connection to represent a {@link Connection} for tests.