Remove unused member aPrefVisiLayers

The only users were removed 18-Nov-2011 in
commit ddb1d5eb, Felix Zhang.

Change-Id: I3843d278881203f63f5daf24a3acf27b7d1f4aa9
Reviewed-on: https://gerrit.libreoffice.org/55562Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

include/svx/svdpage.hxx

@@ -430,7 +430,6 @@ protected:
     // new MasterPageDescriptorVector
     std::unique_ptr<sdr::MasterPageDescriptor> mpMasterPageDescriptor;
 
-    SdrLayerIDSet       aPrefVisiLayers;
     sal_uInt16          nPageNum;
 
     bool                mbMaster : 1;               // flag if this is a MasterPage

svx/source/svdraw/svdpage.cxx

@@ -1146,14 +1146,12 @@ SdrPage::SdrPage(SdrModel& rModel, bool bMasterPage)
     mpSdrPageProperties(nullptr),
     mxUnoPage(),
     mpMasterPageDescriptor(nullptr),
-    aPrefVisiLayers(),
     nPageNum(0),
     mbMaster(bMasterPage),
     mbInserted(false),
     mbObjectsNotPersistent(false),
     mbPageBorderOnlyLeftRight(false)
 {
-    aPrefVisiLayers.SetAll();
     mpSdrPageProperties.reset(new SdrPageProperties(*this));
 }
 
@@ -1209,7 +1207,6 @@ void SdrPage::lateInit(const SdrPage& rSrcPage)
     // the contained objects
     mbMaster = rSrcPage.mbMaster;
     mbPageBorderOnlyLeftRight = rSrcPage.mbPageBorderOnlyLeftRight;
-    aPrefVisiLayers = rSrcPage.aPrefVisiLayers;
     mnWidth = rSrcPage.mnWidth;
     mnHeight = rSrcPage.mnHeight;
     mnBorderLeft = rSrcPage.mnBorderLeft;