Chemical inventory item content type update.

- updated to work with chemical inventory item content type
- removed now unnecessary code
- replaced 'und' with constant LANGUAGE_NONE as per Drupal standards
- fixed instance of the code being called on new node creation
- removed resetting of expire date on MSDS URL edit, now only a change in MSDS file will trigger a reset

Signed-off-by: ekennedy <evkennedy@upei.ca>