future-util: fix do_until() API to not have forwarding references
future-util: fix do_until() API to not have forwarding references

The implementation copies lvalues rather than forwards them, and
multiple callers depend on this. It's also saner, so fix the API
to not use forwarding references. Instead, assume moves and require
callers who need reference semantics to use std::ref().
Message-Id: <2ee4b128c26b8fac0690917a224732cf42c5c4e5@scylladb.com>

cloudius-systems/seastar,scylladb/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,dreamsxin/seastar,avikivity/seastar,avikivity/seastar,dreamsxin/seastar,cloudius-systems/seastar,cloudius-systems/seastar,scylladb/seastar,dreamsxin/seastar,syuu1228/seastar,avikivity/seastar