Bug 9827: remove 'insecure' system preference

Bug 9827: remove 'insecure' system preference

This patch removes 'insecure' system preference.

Also removes remaining code that make use of
the preference. It's broken anyway.

Only remains a reference in POD of C4/Boolean.pm

To test:
1) If you like, enable 'insecure' syspref. Broken system.
WARN: be prepared to revert value in database.

2) Apply the patch

3) Run updatedatabase.pl

4) Check that Staff login proceeds as usual.

5) Check that 'insecure' syspref is no more.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Amended patch: Remove 2 occurrences of insecure (in comment only)
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>