ScScenarioFlags
add ScScenarioFlags::NONE for 0.
replace uses of '-= flag' with '&= ~flag'.

Change-Id: I003c0ca1f59b060f52935fec8bb6282fd9981805
Reviewed-on: https://gerrit.libreoffice.org/27464Tested-by: Jochen Nitschke <j.nitschke+logerrit@ok.de>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>