Bug 28317: Use the default CGI::Session serializer

Bug 28317: Use the default CGI::Session serializer

We remove YAML::Syck on bug 22824 and YAML on 27673, to use YAML::XS.
However we need one of them for CGI::Session::Serialize::yaml
It's preferable to change the serializer and use the default one instead
of writing one based on YAML::XS (or patch the existing ::yaml that does
not seem maintained).

There was an encoding bug reported on the default serializer (see commit
a858e8a8b895640f2) but we fail to recreate it.

Test plan:
Create 3 libraries with branchcode=branchname: "CPL", "ÄÄÄ~ÄãÃ" and "✔️ ❤️ ★"
Use the 3 options of SessionStorage and switch from one logged in
library to another.
Confirm that everything is working correctly (ie. no ending issue in the
library name at the top-right corner)

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>