Bug 11433: (code cleanup) remove unused 'attachbasket' op value in basket.pl

This patch cleans code in basket.pl

In basket.pl, some code is supposed to be executed if
$op eq 'attachbasket'. But it is never the case
(grep attachbasket * -r), so this condition can be removed.

No functional change expected.

Regression test only :
* Make a complete acquisition process, from the creation of a basket
 to the closure of a basketgroup, and check everything is OK
* On a basket page, try to change the basketgroup it belongs to, and
  check everything is OK
* On a basketgroup page, try to edit the content of a basketgroup (put
  a new basket in it, change the deliverybranch...), and check everything
  is OK
* On a basketgroup page, try to reopen a closed basketgroup, and close an
  open basketgroup, and check everything is OK

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>