Move react and react-dom to dev dependencies

[stackptr]

react and react-dom are only needed to run Jest tests. Otherwise, react is expected to be provided from the existing peer dependency in consumer packages.

[stackptr]

Before:

❯ yarn why react-dom -R
└─ @freckle/student-materials@workspace:.
   └─ @freckle/react-hooks@npm:5.2.0 [b78f6] (via npm:^5.2.0 [b78f6])
      └─ react-dom@npm:18.2.0 [e4050] (via npm:^18.2.0 [e4050])

After pointing to this branch, yarn why react-dom has no output.