refactor: migrate ENABLE_CSMH_EXTENDED off FEATURES-as-dict in the CSM bigint migration

ENABLE_CSMH_EXTENDED is a flat setting (openedx/envs/common.py, default True); its app
readers (courseware/models.py) and tests already use settings.ENABLE_CSMH_EXTENDED. The
2019 0011_csm_id_bigint data migration still read settings.FEATURES["ENABLE_CSMH_EXTENDED"]
in two places:
- the Migration class body, evaluated at import time (on every migrate / makemigrations /
  test-DB build), gating an extra dependency; and
- database_forwards(), gating the studentmodulehistoryextended ALTER TABLE.

Switch both to bare settings.ENABLE_CSMH_EXTENDED, matching models.py. Behavior is
identical, and reading the flat setting keeps the migration working for the deployments
that still apply it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: feanil

lms/djangoapps/courseware/migrations/0011_csm_id_bigint.py

@@ -21,7 +21,7 @@ def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.model_name)
 
         if schema_editor.connection.alias == 'student_module_history':
-            if settings.FEATURES["ENABLE_CSMH_EXTENDED"]:
+            if settings.ENABLE_CSMH_EXTENDED:
                 if schema_editor.connection.vendor == 'mysql':
                     schema_editor.execute("ALTER TABLE `coursewarehistoryextended_studentmodulehistoryextended` MODIFY `student_module_id` bigint UNSIGNED NOT NULL;")
                 elif schema_editor.connection.vendor == 'postgresql':
@@ -45,7 +45,7 @@ class Migration(migrations.Migration):
         ('courseware', '0010_auto_20190709_1559'),
     ]
 
-    if settings.FEATURES["ENABLE_CSMH_EXTENDED"]:
+    if settings.ENABLE_CSMH_EXTENDED:
         dependencies.append(('coursewarehistoryextended', '0002_force_studentmodule_index'))
 
     operations = [