Workhorse: Stop generating MD5 hashes for filenames

In https://gitlab.com/gitlab-org/gitlab/blob/95d9c5fd8d888af95798bffa18ef55506ef2f8a0/workhorse/internal/upload/destination/multi_hash.go#L14, we generate hashes for file uploads in MD5, SHA1, SHA256, and SHA512.

For FIPS compliance, we need to drop MD5 support. If this is needed non non-FIPS builds (e.g. for Maven packages), we can conditionally do this via fips.Check().