Rothamsted Core Permissions: Remove previous user types

[aislinnpearson]

Following on from issue #373 a reminder to delete the old user types once everyone on the system has been updated to the new user types.

[paul121]

Specifically we only need to remove the farmOS core roles (Manager, Worker and Viewer), which can be done by uninstalling the core farm_role_roles module. @aislinnpearson after the deploy is complete and you have updated user roles, assign this issue to @mstenta for him to do make the change

[mstenta]

Done!