🔥 rip out VLLM_SPYRE_TEST_BACKEND_LIST

[prashantgupta24]

Description

We anyway use markers for selecting the tests so this env var wasn't useful

[github-actions]

👋 Hi! Thank you for contributing to vLLM support on Spyre.
Just a reminder: Make sure that your code passes all the linting checks, otherwise your PR won't be able to be merged. To do so, first install the linting requirements, then run format.sh and commit the changes. This can be done with uv directly:

uv sync --frozen --group lint --active --inexact

Or this can be done with pip:

uv pip compile --group lint > requirements-lint.txt
pip install -r requirements-lint.txt
bash format.sh

Now you are good to go 🚀

[prashantgupta24]

I guess I could simplify this function more, but it does feel more readable this way 🤷

[joerunde]

🌶️ !!!

[joerunde]

Low risk test-only changes, let's get it in