Bug 14330: Remove unused email_sender from sendbasket/sendshelf

Bug 14330: Remove unused email_sender from sendbasket/sendshelf

The sendbasket/sendshelf scripts and templates do not use email_sender
as a cgi parameter or as a template var. Probably a leftover from previous
changes.
Let's make Koha cleaner :)

Test plan:
[1] Send your cart from opac or staff.
[2] Send a shelf from opac or staff.
[3] Git grep email_sender. No results.

Followed test plan. Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>