fix a mistake that I put a broken version into stable tree, I added a line that shouldn't be there

cat.c

@@ -5,10 +5,8 @@
 #include <stdlib.h>
 #include<sys/stat.h>
 #include<string.h>
-#include<windows.h>
 int main(int argc,char *argv[])
 {
-
     if(argc==1) {
 read_from_stdin();
 return 0;