Remove flash-attn from vllm extra (#542)

pyproject.toml

@@ -66,7 +66,7 @@ mistralai = ["mistralai >= 0.1.0"]
 ollama = ["ollama >= 0.1.7"]
 openai = ["openai >= 1.0.0"]
 vertexai = ["google-cloud-aiplatform >= 1.38.0"]
-vllm = ["vllm >= 0.2.1", "filelock >= 3.13.4", "flash-attn >= 2.5.7"]
+vllm = ["vllm >= 0.2.1", "filelock >= 3.13.4"]
 
 [project.urls]
 Documentation = "https://distilabel.argilla.io/"