Remove anchors/hashes in Snowplow events URLs

What does this MR do and why?

Related to #341882 (closed)

This MR removes the URL hash/fragment from Snowplow events, so we avoid adding unmasked PII data.

How to set up and validate locally

1. Follow the instructions in our docs to enable Snowplow locally, if you haven't done so.
2. Turn on the mask_page_urls feature flag.
3. Browse to a page that includes a hash to trigger a Page View Snowplow event. For example, you can go to http://127.0.0.1:3000/gitlab-org/gitlab-test/edit#js-general-settings.
4. Verify the Snowplow testing tool of your choice, no hashes should be found.

MR acceptance checklist

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