Bug 30731: Remove Readonly::XS::MAGIC_COOKIE

Bug 30731: Remove Readonly::XS::MAGIC_COOKIE

This variable does not make sense anymore, since the Readonly::XS
module is not listed in the cpanfile. So it will not be required
the versions_info loop.

Test plan:
Run t/Installer_PerlModules.t again.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 900aa4bf51b131c9f362cb647edf1bb0de2fbcc0)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>