backupccl: remove stitching queue file count ceiling

This change removes the maxQueueSize that limited the number
of files that could be buffered in the queue when merging
SSTs during a backup. The efficacy and need of this cap
is not evident, and we already have a byte limit on how
large the queue can grow. This reduces the number of
variables that need to be tuned to achieve more optimal file
merging behaviour.

Release note: None

pkg/ccl/backupccl/backup_processor.go

@@ -91,10 +91,6 @@ var (
 	)
 )
 
-// maxSinkQueueFiles is how many replies we'll queue up before flushing to allow
-// some re-ordering, unless we hit smallFileBuffer size first.
-const maxSinkQueueFiles = 24
-
 const backupProcessorName = "backupDataProcessor"
 
 // TODO(pbardea): It would be nice if we could add some DistSQL processor tests
@@ -608,7 +604,7 @@ func (s *sstSink) push(ctx context.Context, resp returnedSST) error {
 	s.queue = append(s.queue, resp)
 	s.queueSize += len(resp.sst)
 
-	if len(s.queue) >= maxSinkQueueFiles || s.queueSize >= int(smallFileBuffer.Get(s.conf.settings)) {
+	if s.queueSize >= int(smallFileBuffer.Get(s.conf.settings)) {
 		sort.Slice(s.queue, func(i, j int) bool { return s.queue[i].f.Span.Key.Compare(s.queue[j].f.Span.Key) < 0 })
 
 		// Drain the first half.