ulimit -R missing; --help is out of sync

[Denys Vlasenko]

According to the source, -R should be setting RLIMIT_RTTIME,
but it does not work:

bash-5.0$ ulimit -R
bash: ulimit: -R: invalid option
ulimit: usage: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]

..and looking at the above help, I notice letters I never saw.
Lets try them?

bash-5.0$ ulimit -b
bash: ulimit: -b: invalid option
ulimit: usage: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
bash-5.0$ ulimit -k
bash: ulimit: -k: invalid option
ulimit: usage: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
bash-5.0$ ulimit -P
bash: ulimit: -P: invalid option
ulimit: usage: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
bash-5.0$ ulimit -T
bash: ulimit: -T: invalid option
ulimit: usage: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]

They probably should not be in help if they don't work.