[Checkins] [zopefoundation/persistent] f80c7b: Remove faulty assertion in PersistentMapping.clear().

[Jason Madden]

  Branch: refs/heads/issue129
  Home:   https://github.com/zopefoundation/persistent
  Commit: f80c7b78d0a331eec510eb3155f1c09d2e411323
      https://github.com/zopefoundation/persistent/commit/f80c7b78d0a331eec510eb3155f1c09d2e411323
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2020-03-12 (Thu, 12 Mar 2020)

  Changed paths:
    M CHANGES.rst
    M persistent/mapping.py
    M persistent/tests/test_mapping.py

  Log Message:
  -----------
  Remove faulty assertion in PersistentMapping.clear().

If there's no jar, we can't be _p_changed.

Fixes #139.