BUG-582: do not call hashCode() from IdentifiableItem.equals()

This call would make sense if we had cached hashCode -- but we do not.
We have two options here, either cache hashCode, or not call it from
equals().

Tracing ODL identified that the only other caller of
hashCode() is HashCodeBuilder.nextHashCode() -- thus the hash code is
used only once.

So caching it would add useless overhead of 4 bytes -- so let's just say
no to that.

Change-Id: I19ae0e5025fb6aec5b4d1019b55976ca5ca2e9d4
Signed-off-by: Robert Varga <rovarga@cisco.com>