qmp: Deprecate 'singlestep' member of StatusInfo

qmp: Deprecate 'singlestep' member of StatusInfo

The 'singlestep' member of StatusInfo has never done what the QMP
documentation claims it does.  What it actually reports is whether
TCG is working in "one guest instruction per translation block" mode.

We no longer need this field for the HMP 'info status' command, as
we've moved that information to 'info jit'.  It seems unlikely that
anybody is monitoring the state of this obscure TCG setting via QMP,
especially since QMP provides no means for changing the setting.  So
simply deprecate the field, without providing any replacement.

Until we do eventually delete the member, correct the misstatements
in the QAPI documentation about it.

If we do find that there are users for this, then the most likely way
we would provide replacement access to the information would be to
put the accelerator QOM object at a well-known path such as
/machine/accel, which could then be used with the existing qom-set
and qom-get commands.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20230417164041.684562-11-peter.maydell@linaro.org