fsmonitor: avoid needless instantiation of dirstate
Using repo.local() instead of util.safehasattr(repo, 'dirstate') also
avoids executing setup procedures for remote repository (including
statichttprepo).
This is reason why this patch also removes a part of subsequent
comment, and try/except for AttributeError at accessing to repo.wvfs.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown