build: modernize with "go fix -stringsseq": use SplitSeq iterators

fs/rc/rcserver/rcserver.go

@@ -233,7 +233,7 @@ func (s *Server) handlePost(w http.ResponseWriter, r *http.Request, path string)
 
 	// Check for Prefer: respond-async header (RFC 7240)
 	preferAsync := false
-	for _, pref := range strings.Split(r.Header.Get("Prefer"), ",") {
+	for pref := range strings.SplitSeq(r.Header.Get("Prefer"), ",") {
 		if strings.EqualFold(strings.TrimSpace(pref), "respond-async") {
 			preferAsync = true
 			in["_async"] = true

fs/sync/sync_test.go

@@ -3114,7 +3114,7 @@ func testLoggerVsLsf(ctx context.Context, fdst, fsrc fs.Fs, logger *bytes.Buffer
 // not be compared against the hash the logger predicted.
 func blankMissingHashes(logger, lsf *bytes.Buffer) {
 	noHash := map[string]bool{}
-	for _, line := range bytes.Split(lsf.Bytes(), []byte("\n")) {
+	for line := range bytes.SplitSeq(lsf.Bytes(), []byte("\n")) {
 		elements := bytes.SplitN(line, []byte(";"), 4)
 		if len(elements) == 4 && len(elements[1]) == 0 {
 			noHash[string(elements[3])] = true