Remove 'inline' from the destructor

[ghost]

When compiling with GCC using -Winline the compiler warns that the call to the destructor will not be inlined (I use ThreadPool in multiple places):

ThreadPool/ThreadPool.h:87:8: warning: inlining failed in call to 
‘ThreadPool::~ThreadPool() noexcept’: call is unlikely and code size would grow [-Winline]
 inline ThreadPool::~ThreadPool()

Besides, there is no reason in inline here. Removing it.

[jhasse]

I hope you're okay with that I cherry-picked your commit on my fork: jhasse@5c54162 :)

[ghost]

Sure! :)