remove unused functions

weed/storage/backend/backend.go

@@ -19,7 +19,6 @@ type BackendStorageFile interface {
 	io.Closer
 	GetStat() (datSize int64, modTime time.Time, err error)
 	String() string
-	Instantiate(src *os.File) error
 }
 
 type BackendStorage interface {

weed/storage/backend/s3_backend/s3_backend.go

@@ -157,10 +157,3 @@ func (s3backendStorageFile S3BackendStorageFile) String() string {
 	return s3backendStorageFile.key
 }
 
-func (s3backendStorageFile *S3BackendStorageFile) GetName() string {
-	return "s3"
-}
-
-func (s3backendStorageFile S3BackendStorageFile) Instantiate(src *os.File) error {
-	panic("implement me")
-}