Sync windows socketpair with Python 3.5+

src/gevent/_socket3.py

@@ -678,9 +678,8 @@ def socketpair(family=None, type=SOCK_STREAM, proto=0):
 else: # pragma: no cover
     # Origin: https://gist.github.com/4325783, by Geert Jansen.  Public domain.
 
-    # gevent: taken from 3.6 release. Expected to be used only on Win. Added to Win/3.5
-    # gevent: for < 3.5, pass the default value of 128 to lsock.listen()
-    # (3.5+ uses this as a default and the original code passed no value)
+    # gevent: taken from 3.6 release, confirmed unchanged in 3.7 and
+    # 3.8a1. Expected to be used only on Win. Added to Win/3.5
 
     _LOCALHOST = '127.0.0.1'
     _LOCALHOST_V6 = '::1'
@@ -703,7 +702,7 @@ def socketpair(family=AF_INET, type=SOCK_STREAM, proto=0):
         lsock = socket(family, type, proto)
         try:
             lsock.bind((host, 0))
-            lsock.listen(128)
+            lsock.listen()
             # On IPv6, ignore flow_info and scope_id
             addr, port = lsock.getsockname()[:2]
             csock = socket(family, type, proto)

src/gevent/tests/test__threading_monkey_in_thread.py

@@ -1,6 +1,6 @@
 # We can monkey-patch in a thread, but things don't work as expected.
 from __future__ import print_function
-import sys
+
 import threading
 from gevent import monkey
 import gevent.testing as greentest

src/gevent/threading.py

@@ -157,7 +157,6 @@ def main_native_thread():
 
         return main_threads[0]
 
-import sys
 if PY3:
     # XXX: Issue 18808 breaks us on Python 3.4+.
     # Thread objects now expect a callback from the interpreter itself