Bug 18706 - Remove useless Javascript

Bug 18706 - Remove useless Javascript

Whe checking a subfield to be deleted, the code
  $(this).val($(this).siblings("[name='subfield']").val());
is useless, the checkbox already contains the subfield code :
  <input type="checkbox" ... name="disable_input" value="[% ite.subfield %]" />

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 6bb4a0405abe0d03be3915644c6a05e2e3ee1e9f)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>