Cloud FS: don't propagate the error if removing a folder returns not found

for Cloud FS the folders are virtual and they, generally, disappear when the
last file is removed.

This fix doesn't work for FTP protocol for now.

Fixes #149

vfs/gcsfs.go

@@ -460,6 +460,11 @@ func (GCSFs) Join(elem ...string) string {
 	return strings.TrimPrefix(path.Join(elem...), "/")
 }
 
+// HasVirtualFolders returns true if folders are emulated
+func (GCSFs) HasVirtualFolders() bool {
+	return true
+}
+
 // ResolvePath returns the matching filesystem path for the specified sftp path
 func (fs GCSFs) ResolvePath(sftpPath string) (string, error) {
 	if !path.IsAbs(sftpPath) {