make: remove targets for building packages for ubuntu wily (end of life)
Ubuntu 15.10 (Wily Werewolf) came out on October 22, 2015 and reached end of
life on July 28, 2016 [1]. Users were encouraged to upgrade to 16.04 (Xenial).
PPA doesn't allow new uploads targeting 15.10 anymore.
[1]: https://wiki.ubuntu.com/Releases
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).