Remove visual tests for the intersection observer component

These tests are flaky by nature and there's very little benefit in visually testing them since the component itself is invisible.

However, I have no idea how to remove these tests, or if we even can.

For example:

This infinitely scrolled list has loaded 60 items in one case, but only 40 in the other. This is because it fetches 20 at a time and may not have finished before the snapshot is taken.

Pipeline failure example: https://gitlab.com/gitlab-org/gitlab-ui/-/jobs/460237942

cc @ealcantara