docs: remove retired Perplexity model provider from supported lists

Author: Claude

SUMMARY.md

@@ -60,7 +60,6 @@
   * [Azure](building-blocks/model-providers/azure.md)
   * [Hugging Face](building-blocks/model-providers/huggingface.md)
   * [OpenAI](building-blocks/model-providers/openai.md)
-  * [Perplexity](building-blocks/model-providers/perplexity.md)
   * [SpiceAI](building-blocks/model-providers/spiceai.md)
   * [XAI](building-blocks/model-providers/xai.md)
 

help/ai-and-models.md

@@ -20,7 +20,6 @@ See [AI Gateway](../features/ai-gateway.md) for full feature details.
 | Azure OpenAI | [Azure](../building-blocks/model-providers/azure.md)              |
 | xAI (Grok)   | [XAI](../building-blocks/model-providers/xai.md)                  |
 | Hugging Face | [Hugging Face](../building-blocks/model-providers/huggingface.md) |
-| Perplexity   | [Perplexity](../building-blocks/model-providers/perplexity.md)    |
 | Spice.ai     | [SpiceAI](../building-blocks/model-providers/spiceai.md)          |
 
 See [Model Providers](../building-blocks/model-providers/) for the complete list.