[INTERNAL] removed "strange" page access from Conf.SummaryWizardPage

The required pages to access the needed data must now be passed into the
CTOR.

Also removed some unneeded null checks.

Change-Id: I851e582ca4d69e5e7a50e909384c2e15d0dc5964
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1912
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>