RFR (S) 8164692: InstanceKlass::_previous_version_count goes negative

[Coleen Phillimore]

Summary: decrement previous_version_count when it's removed from the list.

The previous_version_count was decremented in the wrong place.  This 
contributed to the bug that Dean's just sent out the RFR and the fix is 
essentially contributed by Dean.

Ran jdk/test/java/lang/instrument, and internal closed (colocated and 
non-colocated) redefinition tests.

open webrev at http://cr.openjdk.java.net/~coleenp/8164692.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8164692


Thanks,
Coleen