docs: fix links and remove second banner

[thesmiler]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

links in homepage banner pointed to wrong locations

Issue Number: N/A

What is the new behavior?

fix where the AI event link points to, remove second banner temporarily

Does this PR introduce a breaking change?

• Yes
• No

Other information

[crisbeto]

This PR was merged into the repository. The changes were merged into the following branches:

• main: a7b0620
• 20.3.x: 185ac24

[github-actions]

Deployed adev-preview for 712b86a to: https://ng-dev-previews-fw--pr-angular-angular-63755-adev-prev-ejvmpoad.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

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