Merge pull request matplotlib#20672 from anntzer/mdw

Remove outdated parts of MatplotlibDeprecationWarning docs.

Author: timhoffm

lib/matplotlib/_api/deprecation.py

@@ -18,16 +18,7 @@
 
 
 class MatplotlibDeprecationWarning(DeprecationWarning):
-    """
-    A class for issuing deprecation warnings for Matplotlib users.
-
-    In light of the fact that Python builtin DeprecationWarnings are ignored
-    by default as of Python 2.7 (see link below), this class was put in to
-    allow for the signaling of deprecation, but via UserWarnings which are not
-    ignored by default.
-
-    https://docs.python.org/dev/whatsnew/2.7.html#the-future-for-python-2-x
-    """
+    """A class for issuing deprecation warnings for Matplotlib users."""
 
 
 # mplDeprecation is deprecated. Use MatplotlibDeprecationWarning instead.