[DOCS] Remove out-dated link

[lcawl]

Summary

This PR removes a link to a deleted page.
In particular, it removes a link from https://www.elastic.co/guide/en/kibana/master/docker.html to https://www.elastic.co/guide/en/kibana/master/settings-xpack-kb.html

[skip ci]

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11
- [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

• Documentation was added for features that require explanation or tutorials
  - [ ] Unit or functional tests were updated or added to match the most common scenarios
  - [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-docs

[schersh]

LGTM