swift234

[SR-1421][SourceKit] Remove misleading help text

`sourcekitd-test` does not use LLVM's command line parsing utilities at
all, except to print a help message. However, the help message is
misleading: by default `llvm::cl` explains the `-help`, `-help-hidden`,
and `-version` options are available, but `sourcekitd-test` does not support
any of those.

https://bugs.swift.org/browse/SR-1421 tracks improving
`sourcekitd-test` help output, which will most likely involve migrating
it to LLVM's command line library. In the meantime, remove the
misleading "help" message.

Also, it should be noted that the return value of `1` returned after
printing the help message is not actually translated into a non-zero
exit code for the program. Add a "FIXME" to track the issue for now.