clean up overinclusion in files using TIOCGWINSZ

now that struct winsize is available via sys/ioctl.h once again,
including termios.h is not needed.

src/stdio/__fdopen.c

 #include "stdio_impl.h"
 #include <stdlib.h>
 #include <sys/ioctl.h>
-#include <termios.h>
 #include <fcntl.h>
 #include <errno.h>
 #include <string.h>

src/stdio/__stdout_write.c

 #include "stdio_impl.h"
 #include <sys/ioctl.h>
-#include <termios.h>
 
 size_t __stdout_write(FILE *f, const unsigned char *buf, size_t len)
 {

src/unistd/isatty.c

 #include <unistd.h>
 #include <errno.h>
 #include <sys/ioctl.h>
-#include <termios.h>
 #include "syscall.h"
 
 int isatty(int fd)