Remove access to 'savefig.dpi', use figure.dpi

`ipykernel` now uses `figure.dpi` to control the dpi of the
image to be created. This means that `dpi` property of the
figure object is a reliable source of truth for the users
preferences.

IPython/core/pylabtools.py

@@ -97,9 +97,7 b" def print_figure(fig, fmt='png', bbox_inches='tight', **kwargs):"
     if not fig.axes and not fig.lines:
         return
 
-    dpi = rcParams['savefig.dpi']
-    if dpi == 'figure':
-        dpi = fig.dpi
+    dpi = fig.dpi
     if fmt == 'retina':
         dpi = dpi * 2
         fmt = 'png'