Remove dead code and unused DEFINEs

Closes GH-5073

Author: Girgias

ext/sockets/conversions.c

@@ -36,16 +36,6 @@ struct _WSAMSG {
     WSABUF           Control;			//void *msg_control, size_t msg_controllen
     DWORD            dwFlags;			//int msg_flags
 }
-struct __WSABUF {
-  u_long			len;				//size_t iov_len (2nd member)
-  char FAR			*buf;				//void *iov_base (1st member)
-}
-struct _WSACMSGHDR {
-  UINT        cmsg_len;					//socklen_t cmsg_len
-  INT         cmsg_level;				//int       cmsg_level
-  INT         cmsg_type;				//int       cmsg_type;
-  followed by UCHAR cmsg_data[]
-}
 */
 # define msg_name		name
 # define msg_namelen	namelen
@@ -57,7 +47,6 @@ struct _WSACMSGHDR {
 # define iov_base		buf
 # define iov_len		len
 
-# define cmsghdr		_WSACMSGHDR
 # ifdef CMSG_DATA
 #  undef CMSG_DATA
 # endif