chore($http): remove deprecated responseInterceptors functionality

Code cleanup! response interceptors have been deprecated for some time, and it is confusing to have
two APIs, one of which is slightly "hidden" and hard to see, which perform the same task. The newer
API is a bit cleaner and more visible, so this is naturally preferred.

BREAKING CHANGE:

Previously, it was possible to register a response interceptor like so:

    // register the interceptor as a service
    $provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
      return function(promise) {
        return promise.then(function(response) {
          // do something on success
          return response;
        }, function(response) {
          // do something on error
          if (canRecover(response)) {
            return responseOrNewPromise
          }
          return $q.reject(response);
        });
      }
    });

    $httpProvider.responseInterceptors.push('myHttpInterceptor');

Now, one must use the newer API introduced in v1.1.4 (4ae46814), like so:

    $provide.factory('myHttpInterceptor', function($q) {
      return {
        response: function(response) {
          // do something on success
          return response;
        },
        responseError: function(response) {
          // do something on error
          if (canRecover(response)) {
            return responseOrNewPromise
          }
          return $q.reject(response);
        }
      };
    });

    $httpProvider.interceptors.push('myHttpInterceptor');

More details on the new interceptors API (which has been around as of v1.1.4) can be found at
https://docs.angularjs.org/api/ng/service/$http#interceptors

Closes #7266