remove trailing slash on fs filenames

[esell]

Minor change to fix #5416

Tested with osFS and caddy-fs-s3, and confirmed that path canonicalization redirects still happen successfully.

[mholt]

Beautiful. Thanks for the patch and the testing!

[CLAassistant]

All committers have signed the CLA.

[francislavoie]

Did you test that browse still works correctly? There's a bunch of other code following that line that uses the same variable, and I'm worried any of those other places could have unexpected breakages.

[esell]

The browse scenario was my specific use-case. You can check it out here: https://zines.esheavyindustries.com/ I am using a locally built version of Caddy with this code change to serve it up.