narrow: make dirstateguard back up and restore working copy narrowspec instead We used to have only one narrowspec for the store and the working copy, but now that we have one narrowspec for each, it seems clear that the dirstateguard was supposed to back up and restore the narrowspec associated with the working copy, not the one associated with the store. clearbackup() (for the store narrowspec) is not needed because the presence of the file in localrepository._journalfiles() takes care of that. Differential Revision: https://phab.mercurial-scm.org/D5504