The raw_value/computed_value handoff on WebSchedulerService is no longer
used now that command_message()/command_sendmail() compute synchronously,
so remove the members and the dead block in the scheduler loop.
Also drop the system/message special-case in dispatchCommand(): a
system/message whose value embeds a {url} now blocks at execution time
like any other internal command, so it should be offloaded to the
command worker task (large stack, off the main loop) instead of running
inline. Update the now-stale comments.
Co-authored-by: Proddy <proddy@users.noreply.github.com>
