compaction: STCS: only proceed to trim bucket if interesting
compaction: STCS: only proceed to trim bucket if interesting

In practice, a bucket that needs trimming will be interesting, but
this could be made clearer in the code.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <20220408184419.100827-2-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

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