Revert "Smarter before/after rules with date_format"

Reverts commit that breaks the functionality of using a valid string in the before parameter (e.g. date_format:Y-m-d|before:+1 year), because it tries to parse the before in the required format too, and there's no way to opt out.

I did try to fix it, but because of the complexity in determining whether the date in the before/after field is of the right format, I just decided to take it out altogether.

This reverts commit 8bf4f0fc3b401accf4ec71f7b249cb615ec0e8f2.