remove test__dns.py (covered by test__socket_dns.py)

greentest/test__dns.py

-import greentest
-import socket as real_socket
-from gevent import socket
-
-class TestHostname(greentest.TestCase):
-    switch_expected = False
-
-    def test_gethostbyname_hostname(self):
-        hostname = real_socket.gethostname()
-        real_ip = real_socket.gethostbyname(hostname)
-        ip = socket.gethostbyname(hostname)
-        assert real_ip == ip, (real_ip, ip)
-
-if __name__=='__main__':
-    greentest.main()