patch 9.0.2086: code cleanup for option callbacks needed

patch 9.0.2086: code cleanup for option callbacks needed

Problem:  code cleanup for option callbacks needed
Solution: remove flag os_doskip, it's not necessary, as we can check,
          whether an error message was returned

Remove unnecessary field os_doskip

Callback functions for boolean options set os_doskip immediately before
returning an error message, so os_doskip isn't actually needed.

closes: #13461

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>