before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.
in this change, we define a formatter for
map<timestamp_type, vector<shared_sstable>>. since the operator<<
for this type is only used in the .cc file, and the only use case
of it is to provide the formatter for fmt, so the operator<< based
formatter is remove in this change.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#16163
f99223919a