ruby: mesi: remove owner and sharer fields from directory tags

ruby: mesi: remove owner and sharer fields from directory tags

The directory controller should not have the sharer field since there is
only one level 2 cache. Anyway the field was not in use.  The owner field
was being used to track the l2 cache version (in case of distributed l2) that
has the cache block under consideration.  The information is not required
since the version of the level 2 cache can be obtained from a subset of the
address bits.