py3: don't use dict.iterkeys()
Instead of iterating of dict.iterkeys(), let's iterate of dict as that will be
equivalent and dict.iterkeys() is not present in Python 3.
Differential Revision: https://phab.mercurial-scm.org/D1796
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 ..