clean up

paddle/fluid/platform/device_tracer.cc

@@ -273,7 +273,6 @@ class DeviceTracerImpl : public DeviceTracer {
     proto::Profile profile_pb;
     profile_pb.set_start_ns(start_ns_);
     profile_pb.set_end_ns(end_ns_);
-    std::string kernel_name;
     for (const KernelRecord &r : kernel_records_) {
       if (correlations_.find(r.correlation_id) == correlations_.end()) {
         fprintf(stderr, "cannot relate a kernel activity\n");