Avoid using wxClientDC to redraw grid lines

This only happens when changing whether/how the lines are drawn, so
there should be no performance issue with just repainting the window.

src/generic/grid.cpp

@@ -9091,12 +9091,6 @@ void wxGrid::RedrawGridLines()
     if ( !ShouldRefresh() )
         return;
 
-    if ( GridLinesEnabled() )
-    {
-        DrawAllGridLines();
-    }
-    else // remove the grid lines
-    {
     m_gridWin->Refresh();
 
     if ( m_frozenColGridWin )
@@ -9106,7 +9100,6 @@ void wxGrid::RedrawGridLines()
     if ( m_frozenCornerGridWin )
         m_frozenCornerGridWin->Refresh();
 }
-}
 
 void wxGrid::EnableGridLines( bool enable )
 {