Remove functional index, keep cache-only fix per reviewer feedback

Drop the LOWER(name) functional index and migration to minimize
the change footprint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

awx/main/migrations/0206_add_host_name_lower_index.py

@@ -1,19 +0,0 @@
-from django.db import migrations, models
-from django.db.models.functions import Lower
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('main', '0205_add_ordering_to_instancegroup_and_workflow_nodes'),
-    ]
-
-    operations = [
-        migrations.AddIndex(
-            model_name='host',
-            index=models.Index(
-                Lower('name'),
-                name='main_host_name_lower_idx',
-            ),
-        ),
-    ]

awx/main/models/inventory.py

@@ -19,7 +19,6 @@ from django.core.exceptions import ValidationError
 from django.urls import resolve
 from django.utils.timezone import now
 from django.db.models import Q, Subquery, OuterRef
-from django.db.models.functions import Lower
 
 # REST Framework
 from rest_framework.exceptions import ParseError
@@ -524,9 +523,6 @@ class Host(CommonModelNameNotUnique, RelatedJobsMixin):
         app_label = 'main'
         unique_together = (("name", "inventory"),)  # FIXME: Add ('instance_id', 'inventory') after migration.
         ordering = ('name',)
-        indexes = [
-            models.Index(Lower('name'), name='main_host_name_lower_idx'),
-        ]
 
     inventory = models.ForeignKey(
         'Inventory',