since fedora 38 is EOL. and fedora 39 comes with fmt v10.0.0, also, we've switched to the build image based on fedora 40, which ships fmt-devel v10.2.1, there is no need to support fmt < 10. in this change, we drop the support fmt < 10. Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Closes scylladb/scylladb#21847