these unused includes are identified by clang-include-cleaner. after auditing the source files, all of the reports have been
confirmed.
---
it's a cleanup, hence no need to backport.
Closesscylladb/scylladb#21374
* github.com:scylladb/scylladb:
.github: add gms to iwyu's CLEANER_DIR
gms: remove unused `#include`s