lfs: add the '{oid}' template keyword to '{lfs_files}'
The 'sha256:' prefix is skipped because this seems like the most convenient way
to consume it. Maybe we should also add a '{oid_type}' keyword? Then again,
that can be added in the future if a different algorithm is supported.
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..