refac: rm mariadb dep

Author: tjbck

backend/requirements.txt

@@ -119,7 +119,7 @@ pgvector==0.4.2
 
 PyMySQL==1.1.2
 boto3==1.42.62
-mariadb==1.1.14
+# mariadb==1.1.14 should be added if you want to support MariaDB
 
 pymilvus==2.6.9
 qdrant-client==1.17.0