Doc bug: sched / set

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

The builtins.yo reference to the "sched" command got converted at some
point into a use of the module() macro.  The problem is, that left some
stray text behind which got incorporated on the end of the description
of the "set" builtin:

The tt(sched) builtin is not made available by default when the shell
starts in a mode emulating another shell.  It can be made available
with the command `tt(zmodload -F zsh/sched b:sched)'.

Several choices possible here:

(1) Delete this text entirely.
(2) Move the text from the builtins.yo to mod_sched.yo.
(3) Create an xmodule() macro that accepts a third argument and pass the
    text there, so it appears in the correct item() in builtins.yo

I haven't checked closely for whether there are other cases where (3) may
be wanted.