pikpak: set the NoMultiThreading feature flag to disable multi-thread copy

Before this change the pikpak backend changed the global
--multi-thread-streams flag which wasn't desirable.

Now the machinery is in place to use the NoMultiThreading feature flag
instead.

Fixes #6915

backend/pikpak/pikpak.go

@@ -189,11 +189,6 @@ Fill in for rclone to use a non root folder as its starting point.
 			Help:     "Files bigger than this will be cached on disk to calculate hash if required.",
 			Default:  fs.SizeSuffix(10 * 1024 * 1024),
 			Advanced: true,
-		}, {
-			Name:     "multi_thread_streams",
-			Help:     "Max number of streams to use for multi-thread downloads.\n\nThis will override global flag `--multi-thread-streams` and defaults to 1 to avoid rate limiting.",
-			Default:  1,
-			Advanced: true,
 		}, {
 			Name:     config.ConfigEncoding,
 			Help:     config.ConfigEncodingHelp,
@@ -224,7 +219,6 @@ type Options struct {
 	UseTrash            bool                 `config:"use_trash"`
 	TrashedOnly         bool                 `config:"trashed_only"`
 	HashMemoryThreshold fs.SizeSuffix        `config:"hash_memory_limit"`
-	MultiThreadStreams  int                  `config:"multi_thread_streams"`
 	Enc                 encoder.MultiEncoder `config:"encoding"`
 }
 
@@ -437,10 +431,6 @@ func newFs(ctx context.Context, name, path string, m configmap.Mapper) (*Fs, err
 
 	root := parsePath(path)
 
-	// overrides global `--multi-thread-streams` by local one
-	ci := fs.GetConfig(ctx)
-	ci.MultiThreadStreams = opt.MultiThreadStreams
-
 	f := &Fs{
 		name:    name,
 		root:    root,
@@ -451,6 +441,7 @@ func newFs(ctx context.Context, name, path string, m configmap.Mapper) (*Fs, err
 	f.features = (&fs.Features{
 		ReadMimeType:            true, // can read the mime type of objects
 		CanHaveEmptyDirectories: true, // can have empty directories
+		NoMultiThreading:        true, // can't have multiple threads downloading
 	}).Fill(ctx, f)
 
 	if err := f.newClientWithPacer(ctx); err != nil {

docs/content/pikpak.md

@@ -220,19 +220,6 @@ Properties:
 - Type:        SizeSuffix
 - Default:     10Mi
 
-#### --pikpak-multi-thread-streams
-
-Max number of streams to use for multi-thread downloads.
-
-This will override global flag `--multi-thread-streams` and defaults to 1 to avoid rate limiting.
-
-Properties:
-
-- Config:      multi_thread_streams
-- Env Var:     RCLONE_PIKPAK_MULTI_THREAD_STREAMS
-- Type:        int
-- Default:     1
-
 #### --pikpak-encoding
 
 The encoding for the backend.