util: remove unused ctxmanager
This was meant as a substitute for Python's "with" with multiple
context managers before we moved to Python 2.7. We're now on 2.7, so
we should have no reason to keep ctxmanager. "hg grep --all
ctxmanager" says that it was never used anyway.
Differential Revision: https://phab.mercurial-scm.org/D73
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 (glob)
$ 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 (glob)
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..