column_family: Don't bother closing the flush_queue on stop()

When stopping a column family we issue a flush(), for which we wait.
Since writes are supposed to have stopped coming in, and also new
flush requests, there's no need to call and wait for the flush_queue
to be closed.

Signed-off-by: Duarte Nunes <duarte@scylladb.com>

database.cc

@@ -1073,9 +1073,7 @@ column_family::stop() {
     return when_all(_memtables->request_flush(), _streaming_memtables->request_flush()).discard_result().finally([this] {
         return _compaction_manager.remove(this).then([this] {
             // Nest, instead of using when_all, so we don't lose any exceptions.
-            return _flush_queue->close().then([this] {
-                return _streaming_flush_gate.close();
-            });
+            return _streaming_flush_gate.close();
         }).then([this] {
             return _sstable_deletion_gate.close();
         });