Remove timeout in the main loop

Remove timeout in the main loop

The main loop waits until there is some data to read in file descriptors of
the X server or the pseudo tty. But it uses a timeout in select(), which
causes that st awake each 20 ms, even it doesn't have something to do. This
patch removes this problem removing the timeout, which is not needed.
---
 TODO |    1 -
 st.c |   27 +++------------------------
 2 files changed, 3 insertions(+), 25 deletions(-)