Remove ZONE::ClearFilledPolysList() and fix ZONE::Unfill()

ClearFilledPolysList is redundant and Unfill() was missing the clearing
of m_insulatedIslands

This fixes potential latent bugs in zone unfilling.

pcbnew/tools/pcb_point_editor.cpp

@@ -1293,7 +1293,7 @@ void PCB_POINT_EDITOR::updateItem() const
     case PCB_ZONE_T:
     {
         ZONE* zone = static_cast<ZONE*>( item );
-        zone->ClearFilledPolysList();
+        zone->UnFill();
         SHAPE_POLY_SET& outline = *zone->Outline();
 
         for( int i = 0; i < outline.TotalVertices(); ++i )

pcbnew/tools/zone_filler_tool.cpp

@@ -204,8 +204,7 @@ int ZONE_FILLER_TOOL::ZoneUnfill( const TOOL_EVENT& aEvent )
 
         commit.Modify( zone );
 
-        zone->SetIsFilled( false );
-        zone->ClearFilledPolysList();
+        zone->UnFill();
     }
 
     commit.Push( _( "Unfill Zone" ) );
@@ -223,8 +222,7 @@ int ZONE_FILLER_TOOL::ZoneUnfillAll( const TOOL_EVENT& aEvent )
     {
         commit.Modify( zone );
 
-        zone->SetIsFilled( false );
-        zone->ClearFilledPolysList();
+        zone->UnFill();
     }
 
     commit.Push( _( "Unfill All Zones" ) );

pcbnew/zone.cpp

@@ -190,6 +190,7 @@ bool ZONE::UnFill()
     for( std::pair<const PCB_LAYER_ID, SHAPE_POLY_SET>& pair : m_FilledPolysList )
     {
         change |= !pair.second.IsEmpty();
+        m_insulatedIslands[pair.first].clear();
         pair.second.RemoveAllContours();
     }
 

pcbnew/zone.h

@@ -621,18 +621,6 @@ public:
      */
     bool IsSame( const ZONE &aZoneToCompare );
 
-    /**
-     * Clear the list of filled polygons.
-     */
-    void ClearFilledPolysList()
-    {
-        for( std::pair<const PCB_LAYER_ID, SHAPE_POLY_SET>& pair : m_FilledPolysList )
-        {
-            m_insulatedIslands[pair.first].clear();
-            pair.second.RemoveAllContours();
-        }
-    }
-
     bool HasFilledPolysForLayer( PCB_LAYER_ID aLayer ) const
     {
         return m_FilledPolysList.count( aLayer ) > 0;