narrow: reuse narrowspec.updateworkingcopy() when narrowing
Similar to the previous patch for widening, but here we also need to
teach updateworkingcopy() to forcefully delete files that are not
recorded in the dirstate as clean. That should be safe because the
narrowing command (e.g. hg tracked --removeinclude) has already
checked that the working copy is clean.
Differential Revision: https://phab.mercurial-scm.org/D5511