Remove extra MANAGE caveat for file upload

[andrea-manzi]

As reported by Paul, for FTS transfers the list of caveats requested to the destination contains twice the MANAGE caveat. FTS includes it in the list and the x509-scitokens-issuer adds it again at

https://github.com/scitokens/x509-scitokens-issuer/blob/master/src/x509_token_issuer.cpp#L112

Can we remove this duplicate? or maybe add it if it's not already there?