How to un-publish a Ready For Sale app from store?

Unpublish/Remove from Sale app from apple App Store:

1. Select your app in iTunes Connect.
2. Go to Pricing and Availability in the App Store and Information section
3. Click Remove from Sale under Availability
4. Click Save

The app will disappear from App Store and the status is set to Developer Removed From Sale in iTunes Connect.

Sample/Example Screen https://appstoreconnect.apple.com/apps/1507806314/appstore/pricing

A word of advice: Read iTunes Connect Guide carefully about this point!

You can remove an app from sales or you can delete it... But pay attention!
If you decide to remove an app from sales, you'll be able to put it back on sales but if you choose to delete it you won't be able to restore it because you can't reuse your SKU, Bundle ID or App Name.

To remove your app from sales:

1. Go to your App Summary Page.
2. Click on Price and availability button.
3. Deselect all the stores Availability regions and then save changes or select "Remove from sale".
   

To delete your app:

1. Go to your App Summary Page.
2. Click on Delete Application button.

Note: You can't delete an app if it is ready for sale. First you need to remove your app from sales and then you can delete it.

Go to your app in iTunes Connect, click "Rights and Pricing", then click the link "Or, you can select specific stores here" at the bottom of the page.

On the next page, deselect all stores and save.