Remove outdated notion of property alias priority from docs.

The concept of alias priority was deprecated in 71d725f and has been
removed since then (making normalize_kwargs maintain kwarg order).

Author: anntzer

lib/matplotlib/_api/__init__.py

@@ -270,8 +270,7 @@ class so far, an alias named ``get_alias`` will be defined; the same will
     exception will be raised.
 
     The alias map is stored as the ``_alias_map`` attribute on the class and
-    can be used by `.normalize_kwargs` (which assumes that higher priority
-    aliases come last).
+    can be used by `.normalize_kwargs`.
     """
     if cls is None:  # Return the actual class decorator.
         return functools.partial(define_aliases, alias_d)