optimize addQueryString.exclude for canonical URLs

[hannesbochmann]

The link which is created for the canonical URL should have the cHash and L parameter excluded. (see this post from Dimitry Dulepov)

Otherwise every L parameter could be added to URLs created by TYPO3 which than leads to an exception in realurl. But that's not exactly the problem. After all it's just a wrong configuration to not exclude the L parameter when having multiple languages. config.linkVars should be configured correct and TYPO3 will take care of adding the L parameter to links if the parameter is valid.

Excluding the "L" and "cHash" parameter should not lead to a problem.

(happens in UrlService::getCanonicalUrl())

Is it possible to add those two parameters?