chore: remove references to ONNX and TRT-LLM

[gau-nernst]

While digging through the code, I still see several mentions of ONNX and TRT-LLM. These should be removed

cortex.cpp/engine/utils/engine_constants.h

Lines 17 to 20 in 76b1983

	constexpr const auto kOnnxRepo = "cortex.onnx";
	constexpr const auto kLlamaRepo = "cortex.llamacpp";
	constexpr const auto kTrtLlmRepo = "cortex.tensorrt-llm";
	constexpr const auto kPythonRuntimeRepo = "cortex.python";

cortex.cpp/engine/services/engine_service.cc

Lines 88 to 90 in 76b1983

	if (os == kMacOs && (ne == kOnnxRepo || ne == kTrtLlmRepo)) {
	return cpp::fail("Engine " + ne + " is not supported on macOS");
	}

There is also Python engine which does not work atm (but I guess I will be working on this one...)

cortex engines install python-engine

Failed to fetch engine releases: Failed to get engine release: {"message":"Not Found","documentation_url":"https://docs.github.com/rest/releases/releases#get-the-latest-release","status":"404"}