Remove includes for json where they are no longer needed

include/openspace/properties/propertyowner.h

@@ -25,7 +25,6 @@
 #ifndef __OPENSPACE_CORE___PROPERTYOWNER___H__
 #define __OPENSPACE_CORE___PROPERTYOWNER___H__
 
-#include <openspace/json.h>
 #include <map>
 #include <string>
 #include <vector>
@@ -295,11 +294,6 @@ public:
      */
     void removeTag(const std::string& tag);
 
-    /**
-     * Generate JSON for documentation.
-     */
-    nlohmann::json generateJson() const;
-
 protected:
     /// The unique identifier of this PropertyOwner
     std::string _identifier;