Revert "[IMP] auth_crypt: update to Passlib 1.6"

Unfortunately Ubuntu LTS does not have passlib 1.6 yet,
even though Debian Stable has it now, so for the sake
of making life easier for everybody we'll stick with
passlib 1.5 for one more version.

This reverts commit c950224ef7.

addons/auth_crypt/auth_crypt.py

@@ -14,7 +14,11 @@ default_crypt_context = CryptContext(
     # kdf which can be verified by the context. The default encryption kdf is
     # the first of the list
     ['pbkdf2_sha512', 'md5_crypt'],
-    deprecated=['auto'],
+    # deprecated algorithms are still verified as usual, but ``needs_update``
+    # will indicate that the stored hash should be replaced by a more recent
+    # algorithm. Passlib 1.6 supports an `auto` value which deprecates any
+    # algorithm but the default, but Ubuntu LTS only provides 1.5 so far.
+    deprecated=['md5_crypt'],
 )
 
 class res_users(osv.osv):