archival: avoid touching deprecated gzip name attribute
The existing workaround didn't work when no filename was specified.
If running in a context with warnings enabled and subsecond mtime it gave a
warning:
DeprecationWarning: use the name attribute
$ 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