ecore-con - simplify down to a single libc resolver

ecore-con - simplify down to a single libc resolver

Summary:
this removes the cares/ares based resolver and the compiled-in dns.c
resolver, modified the getaddrinfo based resolver to use threads not
forking (almost halving its size) and now makes that the only resolver
we have. getaddrinfo handles ipv6 and ipv4 (according to docs). this
simplifies code paths, drops code size of the efl tree by about 11k
lines of code, makes it easier to test and more robust to future
changes with ip resolving as it now just relies on libc. we won't have
coverity complaints on dns.c imported code anymore to fix and don't
have tokeep up with bugfixes/security from the upstream imported code.
this means we use a single resolver on all platforms (windows, mac,
linux) as opposed to before where cares was used for windows, and
dns.c on linux/mac. oh and the forking original was broken since our
move to eo too. so it couldnt even compile if enabled, letalone work.

so fix bug with missing /etc/resolv.conf that dns.c couldn't cope
with, fix testability, fix maintainability and reduce efl codebase size.

this fixes T3668

@fix
@improve

Subscribers: cedric, seoz, jpeg

Maniphest Tasks: T3668

Differential Revision: https://phab.enlightenment.org/D3971