It's been replaced with:
1 - Control (right) - click one the file in the Trash bin and select Delete Immediately from the contextual menu.
You'll get the following response:
This works like the Secure Delete as it writes over the file on the HD and will override those files that are said to be still in use by some other app:
2 - also you can select the file wherever it may be on the HD, hold down the Option key and use the File ➙ Delete Immediately menu option to delete and overwrite the file without first having to drag it to the Trash bin in the Dock: