You can‘t remove the feature completely. It‘s possible to disable almost all of its features.
In the Settings app, go to Siri & Search. At the top, you‘ll find “Ask Siri”. There, open “Listen for” and make sure to select Off. Below “Listen for”, disable “Press Side Button for Siri”. Then go to “Messaging with Siri“ and disable Automatically Send Messages.
Under “Ask Siri”, there’s “Before Searching”. Go to “Show Suggestions” and disable it.
Further down in Siri & Search, you’ll find “Suggestions from Apple”. Turn off all four of them.
Below that, you’ll find a list of apps. You’ll have to select every single app, and toggle off everything you find there.