Drop cub::Mutex (NVIDIA#3251)

Fixes: NVIDIA#3250

Author: bernhardmgruber

cub/cub/host/mutex.cuh

@@ -402,23 +402,23 @@ THRUST_RUNTIME_FUNCTION typename get_plan<Agent>::type get_agent_plan(int ptx_ve
 #  ifdef __CUDA_ARCH__
     plan = get_agent_plan_dev<Agent>();
 #  else
-    static cub::Mutex mutex;
+    static std::mutex mutex;
     bool lock = false;
     if (d_ptr == 0)
     {
       lock = true;
       cudaGetSymbolAddress(&d_ptr, agent_plan_device);
     }
     if (lock)
-      mutex.Lock();
+      mutex.lock();
     f<<<1,1,0,s>>>((AgentPlan*)d_ptr);
     cudaMemcpyAsync((void*)&plan,
                     d_ptr,
                     sizeof(AgentPlan),
                     cudaMemcpyDeviceToHost,
                     s);
     if (lock)
-      mutex.Unlock();
+      mutex.unlock();
     cudaStreamSynchronize(s);
 #  endif
     return plan;