the formatter for sstables::generation_type does not support "d"
specifier, so we should not use "{:d}" for printing it. this works
before d7c90b5239, but after that
change, generation_type is not an alias of int64_t anymore.
and its formatter does not support "d", so we should either
specialize fmt::formatter<generation_type> to support it or just
drop the specifier.
since seastar::format() is using
```c++
fmt::format_to(fmt::appender(out), fmt::runtime(fmt), std::forward<A>(a)...);
```
to print the arguments with given fmt string, we cannot identify
these kind of error at compile time.
at runtime, if we have issues like this, {fmt} would throw exception
like:
```
terminate called after throwing an instance of 'fmt::v9::format_error'
what(): invalid format specifier
```
when constructing the `std::runtime_error` instance.
so, in this change, "d" is removed.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#14427
04434c02b3