Update documentation for `$httpBackend`

In the sample code's `beforeEach()` function, the dependencies were retrieved directly from `$injector`. Instead, they can be injected into the function directly. AngularJS will resolve `_name_` as though it were `name`, which allows us to use the `name` format for our own variables. This isn't necessary for `$controller`, as we don't need to save this anywhere, just use it in the `beforeEach()`.