Removes copy form VariableValue

On `Use std::shared_ptr for variable resolution` @WGH changes
VariableValue to be a shared_ptr. As shared pointer, the copy
on AnchoredVariable is no longer necessary. The copy was removed
along with the copy constructor.

headers/modsecurity/anchored_variable.h

@@ -79,7 +79,7 @@ class AnchoredVariable {
     std::string m_value;
 
  private:
-    VariableValue m_var;
+    std::shared_ptr<VariableValue> m_var;
 };
 
 }  // namespace modsecurity