Some of the apps can be removed. You'll have to do this on your iPhone. Go to the Watch app, and select the "My Watch" tab. Scroll down until you find the apps visible on your Apple Watch. There's a large number of apps, such as Contacts, Activity, Phone, ... that can't be removed. You'll find a gap between apps, though:
The apps below that gap can be removed, so you won't see them on your Apple Watch. Tap one of them, then you'll find this:
When you disable it, the app will disappear from your Apple Watch.