Bug 35663: Reword default privacy option in opac-privacy.pl

Bug 35663: Reword default privacy option in opac-privacy.pl

This patch updates the description of the OPAC privacy page, replacing:

"Default: keep my history according to local laws. This is the default
option : the library will keep your history for the duration permitted
by local laws."

...with:

"Default: keep my history according to library policy. This is the
default option : the library will keep your history for the duration set
by library policy."

This correctly reflects the fact that privacy is managed according to a
Koha cron configuration.

To test, apply the patch and make sure the OPACPrivacy and related
preferences are enabled.

- Log in to the OPAC and click the "Privacy" tab in the left-hand
  sidebar.
- Confirm that the description of the default privacy option is correct.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>