dagutil: remove heads() and localsubset from revlogdag.__init__
The previous commit removed the last consumer of this API.
I'm not going to mark as API incompatible because I doubt anybody
used this functionality (outside of possibly passing an argument
to revlogdag.__init__). I intend to remove revlogdag later in
this series and its API annotation will cover this one.
Differential Revision: https://phab.mercurial-scm.org/D4320
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1