Bug 14468: followup to fix tests

Bug 14468: followup to fix tests

This patch fix an expected  test result.
Also changes a comparison for the return value to 'delete'
layout sub, in case of success it returns 'undef' and triggers
the message 'use of uninitialized value $del_results ...'

To test:
1) Whitout this patch

prove t/db_dependent/Labels/t_Layout.t

fails.

Also note the message
"Use of uninitialized value $del_results in string ne at t/db_dependent/Labels/t_Layout.t line 110."
for using the return value of delete layout (undef on success!)

2) Apply the patch
3) Test pass and no more message

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>