perf: remove fallbacks to ancient versions of dirstate.walk()
If the call to dirstate.walk() failed, we would try to fall back to
older versions. These were removed in
d3d1d39da2fa (walk: remove
cmdutil.walk, 2008-05-12) and
f8299c84b5b6 (dirstate: fold statwalk
and walk, 2008-06-26). We don't care about testing performance of
versions that old versions at this point, so let's clean up.
Differential Revision: https://phab.mercurial-scm.org/D845
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present