hgcia: remove hgcia (BC)
As discussed at:
https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-March/081018.html,
cia service is down for years. It also uses socket.setdefaulttimeout() which
will break chg. This patch removes the extension.
.. Common link and substitution definitions.
.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html