utils::in uses std::aligned_storage, which is deprecated. Rather than fixing it, replace its only
user with simpler code and remove it.
No backport needed as this isn't fixing a bug.
Closesscylladb/scylladb#19683
* github.com:scylladb/scylladb:
utils: remove utils/in.hh
gossiper: remove initializer-list overload of add_local_application_state()