RFR: 8185746: Remove Mutex destructor assertion

[Kim Barrett]

> On Aug 2, 2017, at 7:31 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
>> On Aug 2, 2017, at 7:23 PM, David Holmes <david.holmes at oracle.com> wrote:
>> 
>> Hi Kim,
>> 
>> On 3/08/2017 8:41 AM, Kim Barrett wrote:
>>> Please review this small change to improve the debugging experience
>>> when a mutex is destroyed in a bad state.
>>> I've removed the assert in ~Mutex, which was making the same checks as
>>> in ~Monitor, but providing much less information.
>> 
>> Okay. Please can you add a comment to the ~Mutex noting that eg:
>> 
>> // Defer any state checking to ~Monitor
>> Mutex::~Mutex() { }
> 
> Well, I was waffling over just removing it completely.

Note also that the structure here makes it pretty easy to accidentally
invoke undefined behavior by destructor slicing. That's an entirely
different problem, but it bugs me...