Remove unnecessary string copy (#2067)

selfdrive/common/swaglog.cc

@@ -93,15 +93,13 @@ void cloudlog_e(int levelnum, const char* filename, int lineno, const char* func
     {"created", seconds_since_epoch()}
   };
 
-  char* log_s = strdup(log_j.dump().c_str());
-  assert(log_s);
+  std::string log_s = log_j.dump();
 
   free(msg_buf);
 
   char levelnum_c = levelnum;
   zmq_send(s.sock, &levelnum_c, 1, ZMQ_NOBLOCK | ZMQ_SNDMORE);
-  zmq_send(s.sock, log_s, strlen(log_s), ZMQ_NOBLOCK);
-  free(log_s);
+  zmq_send(s.sock, log_s.c_str(), log_s.length(), ZMQ_NOBLOCK);
 
   pthread_mutex_unlock(&s.lock);
 }