Don't prevent boot time file system check of root

Manjaro's grub configuration loads / as rw. This prevents / to be checked by fsck at boot time. systemd-fsck-root.service may check root at boot time if required, but only if it's mounted with ro. But, because of this patch, the check is always skipped.

Checking root fs in any other way is not trivial. Take a look at this manjaro forum thread for discussions on this topic.

Even when this flag is to ro in grub, / is mounted as with read-write access eventually at later stages of the boot. It's not clear why this flag should be intentionally set to rw here.