remove unused dynamic settings (#2735)

# What this PR does

While working on https://github.com/grafana/oncall/pull/2734 I removed a
block of code that was the last reference to a dynamic setting
(`enabled_web_schedules_orgs`).

That led me to see which dynamic settings we still have references to
(at the database level), and create this cleanup migration for
deprecated dynamic settings.

## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)

engine/apps/base/migrations/0005_drop_unused_dynamic_settings.py

@@ -0,0 +1,42 @@
+# Generated by Django 3.2.20 on 2023-08-02 17:56
+
+from django.db import migrations
+
+
+def remove_unused_dynamic_settings(apps, schema_editor):
+    """
+    These are deprecated dynamic settings that no longer have references and should be dropped
+    """
+    DynamicSetting = apps.get_model("base", "DynamicSetting")
+
+    DynamicSetting.objects.filter(
+        name__in=[
+            "enabled_web_schedules_orgs",
+            "enabled_mobile_test_push",
+            "enabled_webhooks_2_orgs",
+            "org_id_to_enable_insight_logs",
+            "messaging_backends_enabled_orgs",
+            "mobile_app_settings",
+            "is_grafana_integration_enabled",
+            "skip_web_cache_for_alert_group",
+            "postpone_distribute_alert",
+            "async_alert_creation",
+            "postpone_distribute_alert_task",
+            "postpone_create_alert_task",
+            "simulate_slack_downtime",
+            "skip_invalidate_web_cache_for_alert_group",
+            "enabled_final_schedule_export",
+            "self_hosted_invitations",
+        ]
+    ).delete()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("base", "0004_auto_20230616_1510"),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_unused_dynamic_settings, migrations.RunPython.noop),
+    ]

engine/apps/slack/slack_client/slack_client.py

@@ -12,7 +12,6 @@ from .exceptions import (
     SlackAPIException,
     SlackAPIRateLimitException,
     SlackAPITokenException,
-    SlackClientException,
 )
 from .slack_client_server import SlackClientServer
 
@@ -88,17 +87,6 @@ class SlackClientWithErrorHandling(SlackClient):
         return cumulative_response, cursor, rate_limited
 
     def api_call(self, *args, **kwargs):
-        from apps.base.models import DynamicSetting
-
-        simulate_slack_downtime = DynamicSetting.objects.get_or_create(
-            name="simulate_slack_downtime", defaults={"boolean_value": False}
-        )[0]
-
-        if simulate_slack_downtime.boolean_value:
-            # When slack is down it returns 503 with no response.text which leads to JSONDecodeError.
-            # We handle it in SlackClientServer and raise SlackClientException instead
-            raise SlackClientException("Slack Downtime Simulation")
-
         response = super(SlackClientWithErrorHandling, self).api_call(*args, **kwargs)
 
         if not response["ok"]: