chain: dont check for null settings value in overwriteRwSetting

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

src/node/interfaces.cpp

@@ -834,7 +834,6 @@ class ChainImpl : public Chain
     }
     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;