docs: Redact already-moved information from README

Description

This MR redacts some sections of the README that have already been moved:

• README: ### Self-signed certificate authority (now at https://docs.gitlab.com/ee/editor_extensions/visual_studio_code/ssl.html#use-the-extension-with-a-self-signed-ca)
• README: ### Browse a repository without cloning (now at https://docs.gitlab.com/ee/editor_extensions/visual_studio_code/remote_urls.html#browse-a-repository-in-read-only-mode)
• docs/assets/virtual-workspace.gif (700 KB)

Related Issues

Related to Plan for migrating VS Code user documentation (#1530)

How has this been tested?

Screenshots (if appropriate)

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes