only register updatecheck libs, when this is enabled

Change-Id: If7b882663ab5cd12d4d9ae01e14162f793d8dc8d
Reviewed-on: https://gerrit.libreoffice.org/6757
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>