Once HSH_Unbusy() has been called there is a possibility for
EXP_Remove() to be called before the fetch thread has had a chance to call
EXP_Insert(). By adding a OC_EF_NEW flag on the objects during
HSH_Unbusy(), that is removed again during EXP_Insert(), we can keep track
and clean up once EXP_Insert() is called by the inserting thread if
EXP_Remove() was called in the mean time.

This patch also removes the AZ(OC_F_DYING) in EXP_Insert(), as that is no
longer a requirement.

Fixes: #2999