Lab: edit the External Links section copy

[goplayoutside3]

Staging branch URL: https://pr-7070.pfe-preview.zooniverse.org

Closes https://github.com/zooniverse/front-end-monorepo/issues/3633

Removed the phrase "These links open in a new tab when clicked." External links behave differently in PFE and FEM, so I just removed the related help text in the lab for now. FEM-hosted projects still use parts the PFE lab for the foreseeable future, so lab instructions must make sense to both.

Required Manual Testing

• [ ] Does the non-logged in home page render correctly?
• [ ] Does the logged in home page render correctly?
• [ ] Does the projects page render correctly?
• [ ] Can you load project home pages?
• [ ] Can you load the classification page?
• [ ] Can you submit a classification?
• [ ] Does talk load correctly?
• [ ] Can you post a talk comment?

Review Checklist

• [ ] Does it work in all major browsers: Firefox, Chrome, Edge, Safari?
• [ ] Does it work on mobile?
• [ ] Can you npm ci and app works as expected?
• [ ] If the component is in coffeescript, is it converted to ES6? Is it free of eslint errors? Is the conversion its own commit?
• [ ] Are the tests passing locally and on GitHub Actions?

Optional

• [ ] Have you replaced any ChangeListener or PromiseRenderer components with code that updates component state?
• [ ] If changes are made to the classifier, does the dev classifier still work?
• [ ] Have you resized and compressed any image you've added?
• [ ] Have you added in flow type annotations?
• [ ] Have you followed the Springer guidelines for commit messages?

[coveralls]

coverage: 56.98% (+0.003%) from 56.977% when pulling d98d3ee68695979682716b55ba15be6d6a30b1e9 on edit-external-links-copy into 1cec52a4f0492712626a77156b06373218519238 on master.