Hi there,
The best way to identify if it's already safe to eliminate the 301 redirects from a previous Web migration/redesign is to verify if the old pages (you need to have a list of those old URLs) that were redirected in the past:
- Are still crawled and indexed? (You can check the indexation easily in Google with "site:" directly, and then if you identify these old URLs in Google Search Console Search Analytics, by filtering by pages). If so, which pages? Are they also ranking still well for relevant terms? Which ones? Identify why is still ranking instead of the new version of the page: Is the redirect correctly implemented? Going to a new version that is really relevant? The old pages being linked from internal or external sources that are passing high value? What's the historical and trend of crawling activity of those pages over time? Is it going down? (that you can analyze via logs).
- Are still getting traffic? Identify which source: is it organic search traffic? referral from other sites? You can check this by verifying the URLs activity from the old site version in Google Analytics.
- Are still being linked? A must if you're still ranking with these pages and traffic. Verify which sources are still linking to them and which are the one passing the highest value. Make the most to update these links to go to the new URL versions to stop passing value and traffic to the old URLs.
If you verify that these old URLs are not indexed, nor getting visibility or traffic anymore either from organic search or any other traffic source, then it's ok to eliminate the redirects.
Nonetheless, if they are still getting visibility & traffic you will need to keep the redirects, otherwise you will lose those visitors (and also give a bad user experience). The goal in this case would be to ask the previous questions among others to identify the reason why are they still being indexed, linked, etc. and update the relevant links, content, etc. to change this behavior and help Google to catch up with the URLs migrations.
I hope it helps 