Fix: filter clear url

[ah-net]

This pull request fixes an issue with the clear/remove filter url when using an alp with the same url as the selected filter.

How to reproduce

• Enable ajax navigation
• Use seo path slugs for url strategy
• Make an alp with the same url as an filter + value as part of the url. For example: /merken/4-seasons-outdoor-tuinmeubelen/4-seasons-outdoor-capalbio. This url contains the name of the filter /merken/4-seasons-outdoor.
• When selecting the filter you get an url like: merken/4-seasons-outdoor-tuinmeubelen/4-seasons-outdoor-capalbio/merken/4-seasons-outdoor/
• Go remove the filter or click on the clear all filters button.
• See that the url is not /merken/4-seasons-outdoor-tuinmeubelen/4-seasons-outdoor-capalbio but /-tuinmeubelen/4-seasons-outdoor-capalbio

Because the url contains the filter + value it gets removed. This pull request fixes that. The url part is only removed if it ends with an slash. Or with nothing.

[jansentjeu]

rtrim is currently doing nothing, because the expression result is not used anywhere.
Use this instead of the two new added lines:

$url = str_replace(
    sprintf('%s/', rtrim($currentFilterPath, '/')),
    sprintf('%s/', $newFilterPath),
    $currentUrl
);