doc: correct and normalize --help output of several tools

doc: correct and normalize --help output of several tools

* src/chroot.c (usage): Add "[ARG]" to synopsis.
* src/cut.c (usage): Remove an inconsistent period in an option
description.
* src/du.c (usage): Remove superfluous argument after short option -X.
Also remove inconsistent uppercase and final period.
Use a single indent level for prettiness.
* src/shred.c (usage): Normalize the synopsis.
* src/stty.c (usage): Options -F and --file are alternatives, cannot
both be used.
* src/sum.c (usage): -r does not overrule -s; the last one counts.
* src/uptime.c (usage): Remove inconsistent space from the synopsis.
* src/users.c: Likewise.