syscall: remove WSAEMSGSIZE

CL 92475 added WSAEMSGSIZE const to syscall package. But there
is already copy of WSAEMSGSIZE in internal/syscall/windows.
So delete syscall.WSAEMSGSIZE

Change-Id: I0b81fa5dcf846887a0cb27d8bbd7e250860627b5
Reviewed-on: https://go-review.googlesource.com/106956
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/internal/poll/fd_windows.go

@@ -226,7 +226,7 @@ func (s *ioSrv) ExecIO(o *operation, submit func(o *operation) error) (int, erro
 		if o.errno != 0 {
 			err = syscall.Errno(o.errno)
 			// More data available. Return back the size of received data.
-			if err == syscall.ERROR_MORE_DATA || err == syscall.WSAEMSGSIZE {
+			if err == syscall.ERROR_MORE_DATA || err == windows.WSAEMSGSIZE {
 				return int(o.qty), err
 			}
 			return 0, err

src/syscall/types_windows.go

@@ -27,7 +27,6 @@ const (
 	ERROR_NOT_FOUND           Errno = 1168
 	ERROR_PRIVILEGE_NOT_HELD  Errno = 1314
 	WSAEACCES                 Errno = 10013
-	WSAEMSGSIZE               Errno = 10040
 	WSAECONNABORTED           Errno = 10053
 	WSAECONNRESET             Errno = 10054
 )