remove futures_util::TryStreamExt usage from server
remove futures_util::TryStreamExt usage from server

{ default-features = false, features = ["server"] } was broken due to a
missing dependency on futures_util.
Since only a single, small convenience method was used, its usage is
just replaced so the dependency can be forgone for the server.

abonander/multipart-async,abonander/multipart-async,abonander/multipart-async