cli: Remove deprecated '-singlestep' command line option

cli: Remove deprecated '-singlestep' command line option

This option has been deprecated before the 8.1 release,
in commit 12fd0f41d0 ("Document that -singlestep command
line option is deprecated"). Time to drop it.

Inspired-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240117151430.29235-4-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>