bpo-31904: remove libnet dependency from detect_socket() for VxWorks (GH-23394)

Previously on VxWorks compiling socket extension module needs the libnet to link. Now VxWorks has moved the replied functions to libc. So removing libnet from setup.py.

Author: pxinwr

Misc/NEWS.d/next/Build/2020-11-19-17-01-50.bpo-31904.894dk2.rst

@@ -0,0 +1 @@
+remove libnet dependency from detect_socket() for VxWorks

setup.py

@@ -1132,11 +1132,7 @@ def detect_crypt(self):
     def detect_socket(self):
         # socket(2)
         kwargs = {'depends': ['socketmodule.h']}
-        if VXWORKS:
-            if not self.compiler.find_library_file(self.lib_dirs, 'net'):
-                return
-            kwargs['libraries'] = ['net']
-        elif MACOS:
+        if MACOS:
             # Issue #35569: Expose RFC 3542 socket options.
             kwargs['extra_compile_args'] = ['-D__APPLE_USE_RFC_3542']