dagutil: remove descendantset() and ancestorset()
descendantset() is unused after the previous commit. And
ancestorset() was only used by descendantset(), so it can be removed
as well.
.. api:: descendantset() and ancestorset() removed from dagutil
Use a revset instead when operating on the changelog. Or use
various functionality in the ancestor or dagop modules.
Differential Revision: https://phab.mercurial-scm.org/D4315
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a