Deleting project does not remove the custom field context associated

To replicate:

1. Create a project
2. Create a custom field
3. Select a project in the custom field's context
4. Delete the project

Go back and notice that the * Applicable contexts for scheme* is now Not configured for any context. This can lead to NPE's when used with filters and two dimensional filter statistics portlet.

Very similar to JRA-9303. The same fix can be applied for this bug.