1.4 deprecation from docs

What are you changing in this pull request and why?

Removes v1.4 from the version dropdown Removes info between lastVersion="1.4" blocks Removes firstVersion="1.4" blocks but leaves content Removes some mentions of v1.4 from places where it's not mentioning a requirement

Checklist

[ ] Review the Content style guide so my content adheres to these guidelines.
[ ] For docs versioning, review how to version a whole page and version a block of content.
[ ] Add a checklist item for anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

Adding or removing pages (delete if not applicable):

[ ] Add/remove page in website/sidebars.js
[ ] Provide a unique filename for new pages
[ ] Add an entry for deleted pages in website/vercel.json
[ ] Run link testing locally with npm run build to update the links that point to deleted pages

dbt-labs / docs.getdbt.com

1.4 deprecation from docs #5597

What are you changing in this pull request and why?

Checklist