Messages Shortcuts To Manage Messages
It's now easier to manage messages from people inside the Messages app. This works with iMessage and with text messages inside the stock Messages app on iOS 11.
Swipe from the right to the left and you will now see Hide Alerts and Delete. if you choose Hide Alerts it will put that conversation in Do Not Disturb Mode. That means you won't get notifications for new messages sent to that thread, but you can still see them in the Messages app.
Delete, does exactly what you'd expect. It deletes that conversation completely from your iPhone or iPad.