Fix warnings

gtsam/nonlinear/ExpressionFactor.h

@@ -24,7 +24,9 @@
 #include <gtsam/base/Testable.h>
 #include <gtsam/nonlinear/Expression.h>
 #include <gtsam/nonlinear/NonlinearFactor.h>
+
 #include <numeric>
+#include <utility>
 
 namespace gtsam {
 
@@ -147,7 +149,7 @@ protected:
       noiseModel_->WhitenSystem(Ab.matrix(), b);
     }
 
-    return factor;
+    return std::move(factor);
   }
 
   /// @return a deep copy of this factor
@@ -252,9 +254,6 @@ public:
   // Provide access to the Matrix& version of unwhitenedError:
   using ExpressionFactor<T>::unwhitenedError;
 
-  /// Destructor
-  ~ExpressionFactorN() override = default;
-
   // Don't provide backward compatible evaluateVector(), due to its problematic
   // variable length of optional Jacobian arguments. Vector evaluateError(const
   // Args... args,...);