dirstate: remove the dedicated backup logic
When alone, the dirstate can now take care of its commit/rollback pattern
itself.
When in a transaction, the transaction deal with commit/rollback pattern quite
fine.
Why did you have a dedicated backup logic?
Welcome to Mercurial for Windows!
---------------------------------
For configuration and usage directions, please read the ReadMe.html
file that comes with this package.
Also check the release notes at:
https://mercurial-scm.org/wiki/WhatsNew