test: Delete flaky test test_rate_limiting_registration_view (#36491)

Deleted out of `RegistrationViewTestV1` although the failure was observed
in `RegistrationViewTestV2` which inherits from it.

Deleted according to flaky test process:
https://openedx.atlassian.net/wiki/spaces/AC/pages/4306337795/Flaky+Test+Process

Flaky test ticket:
- https://github.com/openedx/edx-platform/issues/36490

openedx/core/djangoapps/user_authn/views/tests/test_register.py

@@ -1857,38 +1857,6 @@ class RegistrationViewTestV1(
             response = self.client.post(self.url, {"email": self.EMAIL, "username": self.USERNAME})
             assert response.status_code == 403
 
-    @override_settings(
-        CACHES={
-            'default': {
-                'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-                'LOCATION': 'registration_proxy',
-            }
-        }
-    )
-    def test_rate_limiting_registration_view(self):
-        """
-        Confirm rate limits work as expected for registration
-        end point.
-        Note that drf's rate limiting makes use of the default cache
-        to enforce limits; that's why this test needs a "real"
-        default cache (as opposed to the usual-for-tests DummyCache)
-        """
-        payload = {
-            "email": 'email',
-            "name": self.NAME,
-            "username": self.USERNAME,
-            "password": self.PASSWORD,
-            "honor_code": "true",
-        }
-
-        for _ in range(int(settings.REGISTRATION_RATELIMIT.split('/')[0])):
-            response = self.client.post(self.url, payload)
-            assert response.status_code != 403
-
-        response = self.client.post(self.url, payload)
-        assert response.status_code == 403
-        cache.clear()
-
     @override_settings(FEATURES=ENABLE_AUTO_GENERATED_USERNAME)
     def test_register_with_auto_generated_username(self):
         """