ref(crons): Delete Monitor.is_muted database column (stage 4) (#103677)

[NEW-564: There needs to be some way to mute the entire cron
detector](https://linear.app/getsentry/issue/NEW-564/there-needs-to-be-some-way-to-mute-the-entire-cron-detector)

Stage 4 of the migration completes the removal of Monitor.is_muted:

- Adds migration 0013 to physically delete the is_muted column from the
database
- Uses SafeRemoveField with DeletionAction.DELETE to safely drop the
column
- This should be run after Stage 3 has been deployed and validated in
production

This completes the migration from monitor-level muting to
environment-level muting.

Author: evanpurkhiser

migrations_lockfile.txt

@@ -17,7 +17,7 @@ hybridcloud: 0024_add_project_distribution_scope
 
 insights: 0002_backfill_team_starred
 
-monitors: 0012_remove_monitor_is_muted_field
+monitors: 0013_delete_monitor_is_muted_field
 
 nodestore: 0001_squashed_0002_nodestore_no_dictfield
 

src/sentry/monitors/migrations/0013_delete_monitor_is_muted_field.py

@@ -0,0 +1,33 @@
+# Generated by Django 5.2.1 on 2025-11-13 22:11
+
+from sentry.new_migrations.migrations import CheckedMigration
+from sentry.new_migrations.monkey.fields import SafeRemoveField
+from sentry.new_migrations.monkey.state import DeletionAction
+
+
+class Migration(CheckedMigration):
+    # This flag is used to mark that a migration shouldn't be automatically run in production.
+    # This should only be used for operations where it's safe to run the migration after your
+    # code has deployed. So this should not be used for most operations that alter the schema
+    # of a table.
+    # Here are some things that make sense to mark as post deployment:
+    # - Large data migrations. Typically we want these to be run manually so that they can be
+    #   monitored and not block the deploy for a long period of time while they run.
+    # - Adding indexes to large tables. Since this can take a long time, we'd generally prefer to
+    #   run this outside deployments so that we don't block them. Note that while adding an index
+    #   is a schema change, it's completely safe to run the operation after the code has deployed.
+    # Once deployed, run these manually via: https://develop.sentry.dev/database-migrations/#migration-deployment
+
+    is_post_deployment = False
+
+    dependencies = [
+        ("monitors", "0012_remove_monitor_is_muted_field"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="monitor",
+            name="is_muted",
+            deletion_action=DeletionAction.DELETE,
+        ),
+    ]