When cycling next/prev selection, keep only single

We want to have only the current item in the selection rather than all
of them

(cherry picked from commit 62e1169492)

eeschema/net_navigator.cpp

@@ -445,6 +445,7 @@ const SCH_ITEM* SCH_EDIT_FRAME::SelectNextPrevNetNavigatorItem( bool aNext )
             m_netNavigator->EnsureVisible( nextId );
         }
 
+        m_netNavigator->UnselectAll();
         m_netNavigator->SelectItem( nextId );
 
         auto* data = static_cast<NET_NAVIGATOR_ITEM_DATA*>( m_netNavigator->GetItemData( nextId ) );

eeschema/tools/sch_selection_tool.cpp

@@ -3218,6 +3218,7 @@ int SCH_SELECTION_TOOL::SelectNext( const TOOL_EVENT& aEvent )
 
     if( item )
     {
+        ClearSelection();
         select( const_cast<SCH_ITEM*>( item ) );
         m_toolMgr->ProcessEvent( EVENTS::SelectedEvent );
     }
@@ -3240,6 +3241,7 @@ int SCH_SELECTION_TOOL::SelectPrevious( const TOOL_EVENT& aEvent )
 
     if( item )
     {
+        ClearSelection();
         select( const_cast<SCH_ITEM*>( item ) );
         m_toolMgr->ProcessEvent( EVENTS::SelectedEvent );
     }