cache: avoid warming the fnodetags cache after clone
That cache can quite expensive to compute on large repository as not that `hg
clone` is warming all cache, this can introduces a significant slowdown for
clone time[1]. As a stop gap measure introduce a quick fix for
that on stable, skipping the fnodetags cache post-clone.
[1] https://www.mercurial-scm.org/pipermail/mercurial/2021-April/052679.html
Differential Revision: https://phab.mercurial-scm.org/D10695
$ 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