core-bundle/src/Resources/contao/library/Contao/Config.php
public static function remove($strKey)
	{
		$objConfig = static::getInstance();

		if (strncmp($strKey, '$GLOBALS', 8) !== 0)
		{
			$strKey = "\$GLOBALS['TL_CONFIG']['$strKey']";
		}

		$objConfig->delete($strKey);
	}
public static function remove($strKey)
	{
		$objConfig = static::getInstance();

		if (strncmp($strKey, '$GLOBALS', 8) !== 0)
		{
			$strKey = "\$GLOBALS['TL_CONFIG']['$strKey']";
		}

		$objConfig->delete($strKey);
	}
Permanently remove a configuration value

@param string $strKey The short key or full variable name