migrations: Remove pgroonga check for postgres database.

Zulip has only supported postgres for a long time, and this is
unlikely to change, so this code was just extra clutter.

pgroonga/migrations/0001_enable.py

@@ -9,12 +9,12 @@ class Migration(migrations.Migration):
     ]
 
     database_setting = settings.DATABASES["default"]
-    if "postgres" in database_setting["ENGINE"]:
-        operations = [
-            migrations.RunSQL(
-                [
-                    (
-                        """
+
+    operations = [
+        migrations.RunSQL(
+            [
+                (
+                    """
 DO $$BEGIN
 EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public,pgroonga,pg_catalog', %(USER)s, %(SCHEMA)s);
 
@@ -29,12 +29,12 @@ CREATE INDEX zerver_message_search_pgroonga ON zerver_message
   USING pgroonga(search_pgroonga pgroonga.text_full_text_search_ops);
 END$$
 """,
-                        database_setting,
-                    )
-                ],
-                [
-                    (
-                        """
+                    database_setting,
+                )
+            ],
+            [
+                (
+                    """
 DO $$BEGIN
 SET search_path = %(SCHEMA)s,public,pgroonga,pg_catalog;
 
@@ -46,10 +46,8 @@ SET search_path = %(SCHEMA)s,public;
 EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public', %(USER)s, %(SCHEMA)s);
 END$$
 """,
-                        database_setting,
-                    )
-                ],
-            ),
-        ]
-    else:
-        operations = []
+                    database_setting,
+                )
+            ],
+        ),
+    ]