sstable: remove_by_toc_name: always close file and input stream
sstable: remove_by_toc_name: always close file and input stream

Get rid of seastar::async.
Use seastar::with_file to make sure the opened file is always closed
and move in.close() into a .finally continuation.

While at it, make remove_by_toc_name noexcept.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla