rely on conn to enforce DefaultReadConcurrency

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

go/vt/topo/keyspace.go

@@ -209,9 +209,6 @@ func (ts *Server) FindAllShardsInKeyspace(ctx context.Context, keyspace string,
 	if opt == nil {
 		opt = &FindAllShardsInKeyspaceOptions{}
 	}
-	if opt.Concurrency <= 0 {
-		opt.Concurrency = DefaultReadConcurrency
-	}
 
 	// Unescape the keyspace name as this can e.g. come from the VSchema where
 	// a keyspace/database name will need to be SQL escaped if it has special
@@ -298,7 +295,9 @@ func (ts *Server) FindAllShardsInKeyspace(ctx context.Context, keyspace string,
 	)
 
 	eg, ctx := errgroup.WithContext(ctx)
-	eg.SetLimit(int(opt.Concurrency))
+	if opt.Concurrency > 0 {
+		eg.SetLimit(int(opt.Concurrency))
+	}
 
 	for _, shard := range shards {
 		shard := shard