Remove user quotas since iRODS 4.3 doesn't support them

[d-w-moore]

In some future release we may be able to discard or discount iRODS 4.2.x compatibility.

At that point, The set_quota method of irods.manager.UserManager and irods.user.iRODSUser should be removed.

[trel]

or we call it v3.0.0 (perhaps both in honor of Python3 and iRODS 4.3)...