Fix compile warnings and remove unused variables

Change-Id: I7acaee5e9cf218b358ffaf0e3af6067faf6f3d2a

runtime/hsa-runtime/core/runtime/runtime.cpp

@@ -488,7 +488,6 @@ hsa_status_t Runtime::CopyMemory(void* dst, core::Agent* dst_agent, const void*
     return block.agentOwner;
   };
 
-  const bool dst_gpu = (dst_agent->device_type() == core::Agent::DeviceType::kAmdGpuDevice);
   const bool src_gpu = (src_agent->device_type() == core::Agent::DeviceType::kAmdGpuDevice);
   core::Agent* copy_agent = (src_gpu) ? src_agent : dst_agent;