Add ability to remove value from enum type

[hosembafer]

In order to make migration (which is adding new values to an enum type) reversible, I decided to add the ability to remove value from enum.

• I have added tests
• I have made corresponding changes to the documentation

[bibendi]

Thank you! 🚀

[hosembafer]

Thank you! 🚀

Thank you too for this gem!