evolve: kill `--obsolete` and `--old-obsolete` flags for graft
Evolve extension used to add the couple of flags to `hg graft` command for
reasons I don't know but they were deprecated. For the functionality of `hg
graft --old-obsolete`, we have `hg grab` now which can do that.
One more reason to kill this is that we have logic to parse the graftstate,
whereas in core, we are going to change how state files are read and write.
Tweaked the tests a bit to use `hg grab` instead of these flags to make rest of
the test output consistent. Replaced an entry of `hg graft -O` in doc by `hg
grab`.