Bug 6195 : Opac user should not have serial manage tab

PrepareSerialData adds a year of 'manage' for staff display
Opac should not see this
Would be better if it returned a cleaner data structure and
let the template engine handle the display

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>