Clean up src/systty.h macros.

Clean up src/systty.h macros.

* systty.h (EMACS_GET_TTY_PGRP, EMACS_SET_TTY_PGRP, EMACS_GET_TTY)
(EMACS_SET_TTY): Remove unneeded abstraction, instead inline the
definition in all uses.
(EMACS_TTY_TABS_OK): Remove, it has a single user.
* src/sysdep.c (discard_tty_input, child_setup_tty)
(init_sys_modes, tabs_safe_p, reset_sys_modes):
* src/emacs.c (shut_down_emacs):
* src/callproc.c (child_setup):
* src/term.c (dissociate_if_controlling_tty): Inline removed macros.