sandbox: Restore blocking I/O on exit

At present sandbox sets non-blocking I/O as soon as any input is read
from the terminal. However it does not restore the previous state on
exit. Fix this and drop the old os_read_no_block() function.

This means that we always enable blocking I/O in sandbox (if input is a
terminal) whereas previously it would only happen on the first call to
tstc() or getc(). However, the difference is likely not important.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/os.h

@@ -26,16 +26,6 @@ struct sandbox_state;
  */
 ssize_t os_read(int fd, void *buf, size_t count);
 
-/**
- * Access to the OS read() system call with non-blocking access
- *
- * \param fd	File descriptor as returned by os_open()
- * \param buf	Buffer to place data
- * \param count	Number of bytes to read
- * \return number of bytes read, or -1 on error
- */
-ssize_t os_read_no_block(int fd, void *buf, size_t count);
-
 /**
  * Access to the OS write() system call
  *