Removed unused var in tf2 (#735)

Signed-off-by: Alejandro Hernández Cordero <[email protected]>

Author: ahcorde

tf2/src/buffer_core.cpp

@@ -1572,7 +1572,6 @@ void BufferCore::_chainAsVector(
 
   output.clear();  // empty vector
 
-  std::stringstream mstream;
   std::unique_lock<std::mutex> lock(frame_mutex_);
 
   TransformAccum accum;