Fields aren't deleted when uninstalled

Problem/Motivation

When uninstalling the module, the cart_is_non_current field is not deleted.

Steps to reproduce

Install and enable the module. Check that the field 'cart_is_non_current' is on each Order Type in 'Managed fields'.

Uninstall the module, and the fields are still present.

Proposed resolution

Write proper uninstall code to remove module's fields.

Remaining tasks

User interface changes

API changes

Data model changes