context: move contents of committablectx.markcommitted() to workingctx
Same reasoning as previous commits: this function updates the
dirstate. By not updating the dirstate here, we also fix the
close-head test.
Differential Revision: https://phab.mercurial-scm.org/D6365
$ 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