obsolete: remove two unused constants

I'm not sure what these constants were intended for, but they have no
users so it's time to say goodbye.

Differential Revision: https://phab.mercurial-scm.org/D12609

mercurial/obsolete.py

@@ -338,8 +338,6 b' def _fm0decodemeta(data):'
 _fm1nodesha256size = _calcsize(_fm1nodesha256)
 _fm1fsize = _calcsize(_fm1fixed)
 _fm1parentnone = 3
-_fm1parentshift = 14
-_fm1parentmask = _fm1parentnone << _fm1parentshift
 _fm1metapair = b'BB'
 _fm1metapairsize = _calcsize(_fm1metapair)