Simplify termio code.

Simplify termio code.
All non-MSDOS non-WINDOWSNT platforms define HAVE_TERMIOS, so
HAVE_TERMIO code is obsolete.
Replace HAVE_TERMIOS conditionals with !DOS_NT.
* src/systty.h: Do not define HAVE_TCATTR.
Remove HAVE_TERMIO, HAVE_LTCHARS and HAVE_TCHARS code.
Do not define EMACS_HAVE_TTY_PGRP.  Only define
EMACS_GET_TTY_PGRP for !DOS_NT.
* src/sysdep.c: Include sysselect.h unconditionally.  Do not include
sys/ioctl.h and termios.h, systty.h does it.  Use
HAVE_SYS_UTSNAME_H instead of USG as an include guard.
(init_baud_rate): Remove HAVE_TERMIO code.
(child_setup_tty): Remove HAVE_TERMIO code.
(emacs_get_tty, emacs_set_tty): Remove HAVE_TERMIO, HAVE_TCHARS
and HAVE_LTCHARS code.  Use !DOS_NT instead of HAVE_TCATTR.
(new_ltchars, new_tchars): Remove, unused.
(init_sys_modes): Remove HAVE_TERMIO, HAVE_TCHARS and HAVE_LTCHARS
code.  Remove special casing for __mips__, it was a no-op.  Remove
HAVE_TCATTR conditional, it is implied by HAVE_TERMIOS.
(init_sys_modes): Remove HPUX special case.
* src/process.c: Include stdlib.h unconditionally.  Do not include
fcntl.h, systty.h does it.  Remove conditional code for
HAVE_SERIAL, it is always true.
(process_send_signal): Remove HAVE_TERMIOS conditional, it's
always true when SIGNALS_VIA_CHARACTERS is true.
(Fcontinue_process, Fprocess_send_eof): Simplify conditionals:
!WINDOWSNT means HAVE_TERMIOS.
(create_process): Remove HAVE_TERMIOS, it's inside a HAVE_PTYS
conditional, which is true for all HAVE_TERMIOS systems.
* src/keyboard.c (init_keyboard): Do not use HAVE_TERMIO, use !DOS_NT
instead of HAVE_TERMIOS.
* src/emacs.c (shut_down_emacs): Use !defined DOS_NT instead of
EMACS_HAVE_TTY_PGRP.
* src/callproc.c (child_setup): Move EMACS_SET_TTY_PGRP use to the
non-MSDOS, non-WINDOWSNT code, it's only defined for such systems
anyway.