Update vertexai.md

[DecentGradient]

Fix deprecated names, no functional changes

Checklist

• Issue number for this PR: #nnn (required)
• Docs included?: (yes/no; required for all API/functional changes)
• Test units included?: (yes/no; required)
• In a clean directory, yarn install, yarn test run successfully? (yes/no; required)

Description

Code sample

[JGSolutions]

I can use it the same as here?

https://firebase.google.com/docs/ai-logic/get-started?platform=web&api=dev