Update quic.c

Co-Authored-By: Claude <noreply@anthropic.com>

packages/bun-usockets/src/quic.c

@@ -316,12 +316,6 @@ void on_udp_socket_data(struct us_udp_socket_t *s, struct us_udp_packet_buffer_t
 #ifndef UIO_MAXIOV
 #define UIO_MAXIOV 1024
 
-#ifndef _WIN32
-struct mmsghdr {
-    struct msghdr msg_hdr;  /* Message header */
-    unsigned int  msg_len;  /* Number of bytes transmitted */
-};
-#endif
 #endif
 
 /* Server and client packet out is identical */