Remove reliance of NavLinks test on DOM structure

Created by: felixfbecker

We have a test for NavLinks for its render output (important since it has a lot links that need to have the right URL).

This test is coupled to the DOM structure to produce a list of text labels. This is bad, because changes to the DOM structure break the test and require manual updates, which is against our testing goals.

Currently there's an [object Object] in the test.

To prevent this in the future, we should just make it a snapshot test of the render output. The output of this small component should be readable enough to not warrant the downsides of reliance on the structure.