Remove require: phpbb/phpbb from Extensions composer.json files

We currently check require: phpbb/phpbb

	public function validate_require_phpbb()

	{

		if (!isset($this->metadata['require']['phpbb/phpbb']))

		{

			return false;

		}

		return true;

	}

However this blocks using the composer.json file for dependencies of the extension, because no package phpbb/phpbb exists. (Also block stuff like using scrutinizer for code quality and other tools that check the deps)

We should move that to the extra section as we did with the extensions display-name, so extensions can use dependencies correctly.