ref(explore): Remove last_received from attribute context tables (#118562)

Removes `last_received` from the `TraceItemAttributeContext` and
`TraceItemAttributeValueContext` tables. We're going to retrieve
`last_received` from ClickHouse instead (getsentry/snuba#7801), so
there's no need to store it.

These tables are completely empty, so the column can be dropped without
any data concerns.

Fixes
[BROWSE-587](https://linear.app/getsentry/issue/BROWSE-587/remove-last-received-from-attribute-context-tables)

Author: DominikB2014

migrations_lockfile.txt

@@ -7,7 +7,7 @@ will then be regenerated, and you should be able to merge without conflicts.
 
 discover: 0003_discover_json_field
 
-explore: 0009_add_trace_item_attribute_value_context
+explore: 0010_remove_last_received_from_attribute_context
 
 feedback: 0007_cleanup_failed_safe_deletes
 

src/sentry/explore/migrations/0010_remove_last_received_from_attribute_context.py

@@ -0,0 +1,38 @@
+# Generated by Django 5.2.14 on 2026-06-26 14:35
+
+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 = [
+        ("explore", "0009_add_trace_item_attribute_value_context"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="traceitemattributecontext",
+            name="last_received",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        ),
+        SafeRemoveField(
+            model_name="traceitemattributevaluecontext",
+            name="last_received",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        ),
+    ]

src/sentry/explore/models.py

@@ -451,8 +451,6 @@ class TraceItemAttributeContext(DefaultFieldsModel):
 
     created_by_id = HybridCloudForeignKey("sentry.User", null=True, on_delete="SET_NULL")
     updated_by_id = HybridCloudForeignKey("sentry.User", null=True, on_delete="SET_NULL")
-    # When the attribute was last seen in storage. Used to prune stale attributes.
-    last_received = models.DateTimeField(null=True)
 
     class Meta:
         app_label = "explore"
@@ -512,8 +510,6 @@ class TraceItemAttributeValueContext(DefaultFieldsModel):
 
     created_by_id = HybridCloudForeignKey("sentry.User", null=True, on_delete="SET_NULL")
     updated_by_id = HybridCloudForeignKey("sentry.User", null=True, on_delete="SET_NULL")
-    # When the value was last seen in storage. Used to prune stale entries.
-    last_received = models.DateTimeField(null=True)
 
     class Meta:
         app_label = "explore"

tests/sentry/explore/test_models.py

@@ -46,7 +46,6 @@ def test_create_project_scoped(self) -> None:
         assert description.id is not None
         assert description.examples == ["GET", "POST"]
         assert description.additional_context is None
-        assert description.last_received is None
 
     def test_create_org_wide(self) -> None:
         description = TraceItemAttributeContext.objects.create(
@@ -156,7 +155,6 @@ def test_create_project_scoped(self) -> None:
         )
         assert context.id is not None
         assert context.additional_context is None
-        assert context.last_received is None
 
     def test_create_org_wide(self) -> None:
         context = TraceItemAttributeValueContext.objects.create(