remove unsupported tag MaintenanceTitle

Newer versions of the installer framework continue only
with supported tags inside the installer config.xml file.

Change-Id: I87c0e8f079023b5ba7cf7cca248e1fa310b7a97e
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>