[FIX] l10n_it_edi: remove 'Send' button from Customer Invoices

'Send' button meant to send Italian e-invoices are shown
for invoices belonging to non-Italian companies as well.

Since the invoices' are being sent on validating the
invoice itself, Send button means less business here.

Hence removed it.

opw-1945836
closes #31470

closes odoo/odoo#40717

Signed-off-by: Josse Colpaert <jco@openerp.com>