Remove the bootstrap version of QAtomic

Remove the indirection through QAtomicOps and ditch the bootstrap version of QAtomic, leaving only the C++11 version, which then should be inlined into qbasicatomic.h. Only moc and automoc remain as bootstrapped tools, and at least libstdc++ already optimizes std::atomic<> to lock-less versions if the application is single-threaded, so there's no benefit from carrying this now-unnecessary abstraction.