remove mandrill_groups_message_id_field as we decided this could not be used
add mandrill_groups_email_frequency field to user table - not sure if this will be used
removing code that added field to user table to track email frequency preference in favor of a field being created on the custom og membership type we are now creating and using instead of the built in membership type. this means a user, in addition to discussions, will be related to a group with our custom membership type instead of the og default. also had to update the group_group field display formatter on the mandrill_groups_group content type to use our membership type for the subscribe link.