Bug 23315: Some systempreferences can not be edited

Bug 23315: Some systempreferences can not be edited

To test
1/ Go to systempreferences
2/ Notice that SelfCheckHelpMessage IntranetmainUserblock
IntranetCirculationHomeHTML IntranetReportsHomeHTML
StaffLoginInstructions are not editable
3/ Apply patch, refresh page
4/ Now they can be edited

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit 63c23a9eacbe6ba5d61d8f47c5f74a46050338ad)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>