Bug 29056: Remove the demo functionality leftovers

Bug 29056: Remove the demo functionality leftovers

Remove forgotten code of the old legacy demo functionality that was
removed from elsewhere except systempreferences, this code not only
serves no purpose but also is causing some troubles for our customers.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit ed99f0fa0295a488a5cb27e6e80cce063147b1db)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>