## Is your feature request related to a problem?
See [this](https://github.com/PostHog/posthog/pull/9139/files/2754c0fd6633c806def5c328d491421ae7de0c19#diff-7f0217a57a02b6ebd709f6aa7bf43760b2d5a53069aee2b7fea27fdad1caadf1) for more info.


## Describe the solution you'd like

> This is used by django-rest-hooks, the library we use to integrate with Zapier. Specifically, this fires our Zapier integration's Triggers. However, the only trigger that actually matters is the "action_performed" one, and that has been completely delegated to the plugin server for a while. We can remove this Python cruft then, along with django-rest-hooks, but first we need to make sure action_defined and annotation_created actually are unused, and roll out an update to https://github.com/PostHog/posthog-zapier that'd remove those two completely.


## Describe alternatives you've considered

Do nothing
ee/api/test/test_hooks.py
hook_id = "abc123"
        Hook.objects.create(id=hook_id, user=self.user, team=self.team, resource_id=20)
        response = self.client.delete(f"/api/projects/{self.team.id}/hooks/{hook_id}")
        self.assertEqual(response.status_code, 204)
    def test_invalid_target(self):
        data = {"target": "https://hooks.non-zapier.com/abcd/", "event": "action_performed"}
        response = self.client.post(f"/api/projects/{self.team.id}/hooks/", data)
        self.assertEqual(response.status_code, 400)
def test_valid_domain() -> None:
    test_cases = {
        "http://hooks.zapier.com": True,
        "https://hooks.zapier.com": True,
        "http://hooks.zapier.com/something": True,
        "https://hooks.zapier.com/something": True,
        "http://hooks.zapierz.com": False,
        "https://hooks.zapierz.com": False,
        "http://hoos.zapier.com/something": False,
        "https://hoos.zapier.com/something": False,
    }
    for test_input, expected_test_output in test_cases.items():
        test_output = valid_domain(test_input)
        assert test_output == expected_test_output