This now hides one of the ScVbaFormatCondition_BASE::Operator overloads, but
that doesn't get called directly at ScVbaFormatCondition anyway.  (And if it
were, we could add an appropriate using declaration to ScVbaFormatCondition.)

Change-Id: I8440b76a5745c6874f7a3bfcbb4bc4ce5618a4c4