docs: Strip last feature-related subheading

Description

This merge request removes the Clone GitLab projects (https://gitlab.com/gitlab-org/gitlab-vscode-extension/#clone-gitlab-projects) subheading from the README. It's being migrated into the gitlab repo in gitlab!173337 (merged).

It removes one image: docs/assets/git-clone.gif (856 KB).

Related Issues

• Depends on Add cloning info, update command list (gitlab!173337 - merged) merging first
• Related to Plan for migrating VS Code user documentation (#1530 - closed)

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