[v2] xfree86: os-support: drop ununsed POSIX_TTY
Found no evidence that this define is practically used anywhere, aymore. Web research just showed up a single ancient .c file (looks like an Wacom driver) from 1998. Xserver's git history doesn't tell when it actually had been introduced.
Changes v2:
- fixed commit message for political correctness
Edited by Enrico Weigelt, metux IT consult .