graft: factor out function to read graft state in separate function
Fatcoring out the logic in a separate function will help us in adding
conditional logic for different versions of graft state files.
Differential Revision: https://phab.mercurial-scm.org/D3651
state: removing remaining instances of opts class variable
The cmdstate class used to have a class variable opts which used to be a dict
which stored all the data for the state. Recent cleanups removed the use of that
variable. There were couple of instances left which are removed by this patch.
Differential Revision: https://phab.mercurial-scm.org/D3653