chain: dont check for null settings value in overwriteRwSetting

- Just call updateRwSetting it will erase the settings when the new
  value is null.

src/interfaces/chain.h

@@ -363,6 +363,9 @@ public:
     virtual bool updateRwSetting(const std::string& name, const SettingsUpdate& update_function) = 0;
 
     //! Replace a setting in <datadir>/settings.json with a new value.
+    //! Null can be passed to erase the setting.
+    //! This method provides a simpler alternative to updateRwSetting when
+    //! atomically reading and updating the setting is not required.
     virtual bool overwriteRwSetting(const std::string& name, common::SettingsValue value, SettingsAction action = SettingsAction::WRITE) = 0;
 
     //! Delete a given setting in <datadir>/settings.json.

src/node/interfaces.cpp

@@ -834,7 +834,6 @@ public:
     }
     bool overwriteRwSetting(const std::string& name, common::SettingsValue value, interfaces::SettingsAction action) override
     {
-        if (value.isNull()) return deleteRwSettings(name, action);
         return updateRwSetting(name, [&](common::SettingsValue& settings) {
             settings = std::move(value);
             return action;