unregisterStrategy(pluginName, strategyName) {
    const strategy = this.strategies[strategyName];

    if (strategy) {
      if (strategy.owner !== pluginName) {
        throw strategyError.get("unauthorized_removal", strategyName);
      }

      delete this.strategies[strategyName];
      global.kuzzle.passport.unuse(strategyName);
    } else {
      throw strategyError.get("strategy_not_found", strategyName);
    }
  }
Unregister
@param {string} pluginName
@param  {string} strategyName
@throws {PluginImplementationError} If not the owner of the strategy or if strategy
                                    does not exist