Remove redundant links from Snowplow docs

What does this MR do and why?

This removes links to other Snowplow doc pages from the main Snowplow guide page.

These links pointed to other Snowplow pages before the pages were added to the left nav in gitlab-docs!2179 (merged), so the links are now redundant.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #334101 (closed)