8164692: InstanceKlass::_previous_version_count goes negative Summary: decrement previous_version_count when it's removed from the list. Reviewed-by: dcubed, dlong, sspitsyn

^build/
^dist/
^.idea/
nbproject/private/
^webrev
^.hgtip
^.bridge2
^.jib/
.DS_Store
.metadata/
.recommenders/