Revert insights page URL masking handler

What does this MR do and why?

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/342078. Follow-up to !72864 (merged).

This reverts changes from !72864 (merged), since !73593 (merged) fixing the root cause has been merged. I left specs intact as regression tests just in case.

See !72864 (comment 721630438) for investigation and more details.

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