DOC: remove references to mpl docs that do not work in this repo

Author: tacaswell

examples/widgets.py

@@ -6,11 +6,6 @@
 In this example, sliders are used to control the frequency and amplitude of
 a sine wave.
 
-See :doc:`/gallery/widgets/slider_snap_demo` for an example of having
-the ``Slider`` snap to discrete values.
-
-See :doc:`/gallery/widgets/range_slider` for an example of using
-a ``RangeSlider`` to define a range of values.
 """
 import inspect