RFR (XXS) 8202164: Remove some unneeded BoolObjectClosure* is_alive parameters

[Kim Barrett]

> On Apr 24, 2018, at 11:01 AM, coleen.phillimore at oracle.com wrote:
>> src/hotspot/share/code/nmethod.cpp
>> 1039   flush_dependencies(/*delete_immediately*/false);
>> 
>> The preceding comment needs to be updated; there's no longer a closure
>> involved.
> 
> I thought I'd gotten them all.   I changed the comment to this. There's a more thorough comment in flush_dependencies that explains why.
> 
>   // If this work is being done during a GC, defer deleting dependencies from the
>   // InstanceKlass.

s/If/Since/

Otherwise, looks good.  No need for another webrev for the comment changes.