net/libproxy: update to 0.4.17

• mark libproxy-mozjs borken
• add new port for pacrunner
• drop support for python2

Changelog:

• 0.4.16:
  • Port to, and require, SpiderMonkey 68
  • Use closesocket() instead of close() on Windows
  • Add symbol versions - be ready to introduce new APIs as needed
  • Add public px_proxy_factory_free_proxies function
  • Add PacRunner config backend (largely untested; feedback welcome!)
  • Small performance improvements
  • pxgsettings: use the correct syntax to connect to the changed signal (silences annoying output on console)
  • Support python3 up to version 3.9
  • Fix buffer overflow when PAC is enabled (CVE-2020-26154)
  • Rewrite url::recvline to be nonrecursive (CVE-2020-25219)
  • Remove nonfunctional and crashy pacrunner caching
  • Never use system libmodman (no other consumers, not maintained)
• 0.4.17:
  • python bindings: fix "TypeError: argtypes must be a sequence of types" (#125)