vcs: drop subprocessio __del__ - it should no longer be necessary, and it might confuse both users and garbage collector After 8dbe46ca608f, we always explicitly close so resources can be released early. __del__ makes it hard for the garbage collector to clean up, and it is misleading to use it as if it was a reliable "Resource acquisition is initialization" finale.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.