tmpfiles: narrow scope of HAVE_SYSV_COMPAT condition for legacy.conf

tmpfiles: narrow scope of HAVE_SYSV_COMPAT condition for legacy.conf

That file contains a bunch of entries of which only some are related to SysV.
The rest are just "traditional APIs" that need to stay. In particular,
/var/lock a.k.a. /run/lock is used by many programs (LVM, iscsi, alsactl).
Similarly, the README about /var/log is something that should stay as long as
we have people migrating from older systems or using the copiuos documentation
that mentions /var/log/messages.txt on the Internet.

/var/lock/subsys is only used by sysvinit, and our code to support /forcefsck,
/fastboot, and /forcequotacheck is conditionalized on HAVE_SYSV_COMPAT, so
conditionalize those here on HAVE_SYSV_COMPAT too.