fix(common/testing): remove internal MockLocationStrategy from common/testing (#9562)

BREAKING CHANGE:

MockLocationStrategy was intended to be internal only and is now removed
from the `@angular/common/testing` public api.

Use `SpyLocation` from `@angular/common/testing` for location testing.

modules/@angular/common/testing.ts

@@ -7,4 +7,3 @@
  */
 
 export {SpyLocation} from './testing/location_mock';
-export {MockLocationStrategy} from './testing/mock_location_strategy';