dirstate: drop comparison primitive on the timestamp class
All comparison are now managed without using operator :
- the status mtime comparisons is handled by the DirstateItem,
- the fixup reliability check,
- the update "hack".
So we no longer needs the operator and should discourage its usage.
Differential Revision: https://phab.mercurial-scm.org/D11841
(binary:application/octet-stream)