Remove unmaintained library.

README.md

 * [Migrations](https://github.com/icomefromthenet/Migrations) - A migration management library.
 * [PHPMig](https://github.com/davedevelopment/phpmig) - Another migration management library.
 * [Phinx](https://github.com/robmorgan/phinx) - Another database migration library.
-* [Entities](https://github.com/kherge/Entities) - A Doctrine ORM service provider for Silex.
 
 ## NoSQL
 *Libraries for working with "NoSQL" backends.*