react-magma-landing: Remove landing page when docs are updated & redirect https://react-magma.cengage.com/ to latest version

[silvalaura]

When we fully update the react-magma-docs to have the package versions within it (#316), we need to get rid of the landing page.

The goal is for https://react-magma.cengage.com/ to directly link to the latest docs page. We may have to figure out if we need to make any changes to Netlify or change the build scripts in react-magma-docs.

[jwad03]

Blocked by #936