Clean no longer used network layer functions

network_tools.py cleaning before GVA introduction:

• #226 (closed): Get rid of ipaddress dependency
• !186 (closed): Delete no longer used parse_endpoint(), parse_endpoints(), check_port(), check_ip(), endpoint_type()
• Delete check_port() in favour of of DuniterPy's port check in the regex
• Delete best_endpoint_address() in favour of DuniterPy's connection_handler which choose in priority domain, ipv6, then ipv4.