chore(performance): Drop legacy key transactions table (#29074)

Follow up to #29015 to drop the table as it is no longer in use.

migrations_lockfile.txt

@@ -6,5 +6,5 @@ To resolve this, rebase against latest master and regenerate your migration. Thi
 will then be regenerated, and you should be able to merge without conflicts.
 
 nodestore: 0002_nodestore_no_dictfield
-sentry: 0235_add_metricskeyindexer_table
+sentry: 0236_remove_legacy_key_transactions
 social_auth: 0001_initial

src/sentry/discover/models.py

@@ -65,21 +65,6 @@ def set_projects(self, project_ids):
             )
 
 
-class KeyTransaction(Model):
-    __include_in_export__ = False
-
-    # max_length here is based on the maximum for transactions in relay
-    transaction = models.CharField(max_length=200)
-    project = FlexibleForeignKey("sentry.Project", db_constraint=False)
-    owner = FlexibleForeignKey("sentry.User", null=True, on_delete=models.SET_NULL)
-    organization = FlexibleForeignKey("sentry.Organization")
-
-    class Meta:
-        app_label = "sentry"
-        db_table = "sentry_discoverkeytransaction"
-        unique_together = (("project", "owner", "transaction"),)
-
-
 class TeamKeyTransaction(Model):
     __include_in_export__ = False
 

src/sentry/migrations/0236_remove_legacy_key_transactions.py

@@ -0,0 +1,35 @@
+# Generated by Django 2.2.24 on 2021-10-05 20:38
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+    # This flag is used to mark that a migration shouldn't be automatically run in
+    # production. We set this to True for operations that we think are risky and want
+    # someone from ops to run manually and monitor.
+    # General advice is that if in doubt, mark your migration as `is_dangerous`.
+    # Some things you should always mark as dangerous:
+    # - Large data migrations. Typically we want these to be run manually by ops so that
+    #   they can be monitored. Since data migrations will now hold a transaction open
+    #   this is even more important.
+    # - Adding columns to highly active tables, even ones that are NULL.
+    is_dangerous = False
+
+    # This flag is used to decide whether to run this migration in a transaction or not.
+    # By default we prefer to run in a transaction, but for migrations where you want
+    # to `CREATE INDEX CONCURRENTLY` this needs to be set to False. Typically you'll
+    # want to create an index concurrently when adding one to an existing table.
+    # You'll also usually want to set this to `False` if you're writing a data
+    # migration, since we don't want the entire migration to run in one long-running
+    # transaction.
+    atomic = True
+
+    dependencies = [
+        ("sentry", "0235_add_metricskeyindexer_table"),
+    ]
+
+    operations = [
+        migrations.DeleteModel(
+            name="KeyTransaction",
+        ),
+    ]