Fix text summarization quickstart

[gewarren]

• Fixes [UUF] Mention --prerelease flag #45917 (and add info about benefits.md file)
• Use snippet tags instead of range to avoid incorrect lines of code being shown
• Delete two unused files in the image generation project directories
• Removes duplicated quickstart from landing page
• Use updated quickstart names on landing page to avoid redirects

(Hide whitespace changes.)

---

Internal previews

📄 File	🔗 Preview link
docs/ai/index.yml	[linkListType: architecture
docs/ai/quickstarts/evaluate-ai-response.md	Quickstart - Evaluate a model's response
docs/ai/quickstarts/generate-images.md	CustomerIntent: As a .NET developer new to OpenAI, I want deploy and use sample code to interact to learn from the sample code to generate images.
docs/ai/quickstarts/prompt-model.md	docs/ai/quickstarts/prompt-model
docs/ai/quickstarts/structured-output.md	Request a response with structured output
docs/ai/quickstarts/use-function-calling.md	CustomerIntent: As a .NET developer new to OpenAI, I want deploy and use sample code to interact to learn from the sample code how to extend the model using Tools.
docs/azure/index.yml	Azure for .NET developers
docs/index.yml	highlightedContent section (optional)