remove use of private type_printers API

IPython/core/pylabtools.py

@@ -173,13 +173,22 b' def select_figure_format(shell, fmt):'
     png_formatter = shell.display_formatter.formatters['image/png']
 
     if fmt == 'png':
-        svg_formatter.type_printers.pop(Figure, None)
+        try:
+            svg_formatter.pop(Figure)
+        except KeyError:
+            pass
         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png'))
     elif fmt in ('png2x', 'retina'):
-        svg_formatter.type_printers.pop(Figure, None)
+        try:
+            svg_formatter.pop(Figure)
+        except KeyError:
+            pass
         png_formatter.for_type(Figure, retina_figure)
     elif fmt == 'svg':
-        png_formatter.type_printers.pop(Figure, None)
+        try:
+            svg_formatter.pop(Figure)
+        except KeyError:
+            pass
         svg_formatter.for_type(Figure, lambda fig: print_figure(fig, 'svg'))
     else:
         raise ValueError("supported formats are: 'png', 'retina', 'svg', not %r" % fmt)