Since write_config was always called with skiplock=1 except
once, it makes sense to drop this parameter like in
PVE::LXC::write_config . If needed in the future, the
caller can use check_lock before write_config anyway.
The method update_config wrapped update_config_nolock
using lock_config, but to prevent update races the whole
"read config", "do something", "write config" flow was
always protected by lock_config anyway, and update_config
was never called.
Thus, we can safely drop update_config and rename
update_config_nolock to write_config like in PVE::LXC .
