remove MissionKontrol (unmaintained since 2021) (#3700)

- ref. #3558

README.md

@@ -740,7 +740,6 @@ _See also: [dbdb.io - Database of Databases](https://dbdb.io/)_
 - [Directus](https://directus.io/) - An Instant App & API for your SQL Database. Directus wraps your new or existing SQL database with a realtime GraphQL+REST API for developers, and an intuitive admin app for non-technical users. ([Source Code](https://github.com/directus/directus)) `GPL-3.0` `Nodejs`
 - [Mathesar](https://mathesar.org/) - An intuitive UI for managing data collaboratively, for users of all technical skill levels. Built on Postgres – connect an existing DB or set up a new one. ([Demo](https://demo.mathesar.org/), [Source Code](https://github.com/centerofci/mathesar)) `GPL-3.0` `Docker`
 - [MindsDB](https://github.com/mindsdb/mindsdb) - MindsDB is an open source self hosted AI layer for existing databases that allows you to effortlessly develop, train and deploy state-of-the-art machine learning models using standard queries. `GPL-3.0` `Python`
-- [MissionKontrol](https://www.missionkontrol.io) - Configurable admin panel allowing non-technical users to CRUD data on MySQL/PostGRES databases. ([Source Code](https://github.com/Mission-Kontrol/MissionKontrol-rails)) `AGPL-3.0` `Ruby`
 - [NocoDB](https://www.nocodb.com/) - No-code platform that turns any database into a smart spreadsheet. It can be considered as an Airtable or Smartsheet alternative. ([Source Code](https://github.com/nocodb/nocodb)) `GPL-3.0` `Nodejs`