parser: make duplicated functions an error (#8792)

vlib/net/unix/aasocket.c.v

@@ -43,60 +43,3 @@ mut:
 
 struct C.sockaddr_storage {
 }
-
-fn C.socket() int
-
-fn C.setsockopt() int
-
-fn C.htonl() int
-
-fn C.htons() int
-
-fn C.bind() int
-
-fn C.listen() int
-
-fn C.accept() int
-
-fn C.getaddrinfo() int
-
-fn C.connect() int
-
-fn C.send() int
-
-fn C.sendto() int
-
-fn C.recv() int
-
-fn C.recvfrom() int
-
-fn C.shutdown() int
-
-fn C.ntohs() int
-
-fn C.getpeername() int
-
-fn C.inet_ntop(af int, src voidptr, dst charptr, dst_size int) charptr
-
-fn C.WSAAddressToStringA() int
-
-fn C.getsockname() int
-
-// defined in builtin
-// fn C.read() int
-// fn C.close() int
-
-fn C.ioctlsocket() int
-
-fn C.fcntl() int
-
-fn C.@select() int
-
-fn C.FD_ZERO()
-
-fn C.FD_SET()
-
-fn C.FD_ISSET() bool
-
-[typedef]
-struct C.fd_set {}