System tracking feature was deprecated starting with Ansible Tower 3.2. However, you can collect facts by using the fact caching feature. Refer to Fact Caching for more detail. If you upgrade from a version earlier than Ansible Tower 3.0, you will find that your system tracking data (historical facts) has been migrated from MongoDB to PostgreSQL.
If you want to delete the old data in MongoDB, you can do so manually. First, connect to your mongo database using the mongo command line client, then run the following commands:
$ use system_tracking
$ db.runCommand( { dropDatabase: 1 } )
At this point, you can also remove the MongoDB packages.