qapi: Drop bogus command from docs

Commit 87a560c4 added it in the wrong place.  Commit 59a2c4ce added it
in the right place, but didn't remove it from the wrong place.  Do
that now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

docs/qapi-code-gen.txt

@@ -680,8 +680,6 @@ Example:
     out:
         error_propagate(errp, err);
     }
-    $ python scripts/qapi-commands.py --output-dir="qapi-generated" \
-    --prefix="example-" example-schema.json
     $ cat qapi-generated/example-qapi-visit.h
 [Uninteresting stuff omitted...]