[CI/Build]Reduce the time consumption for LoRA tests

[jeejeelee]

The current CI LoRA tests is quite time-consuming, which hampers the development of LoRA-related features. Based on testing on my local single 3090, the three most time-consuming tests are:

case	time
test_punica_variation.py	33minutes
test_layer_variation.py	23minutes
test_punica_sizes.py	10minutes

Therefore, I make the following modifications:

• For test_punica_variation and test_punica_sizes, I reduce the number of test items as much as possible without impacting the test scope.
• I delete test_layer_variation directly, there are two main reasons:
  • Various layers and ranks are tested across different model-related tests, making this script somewhat redundant.
  • In this script, PEFT initializes LoRA weights by setting lora_b weights to zero, this may prevent it from achieving its intended test effects.

Additionally, I clean up some redundant code.

ping @Yard1 @simon-mo

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which consists a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of default ones by unblocking the steps in your fast-check build on Buildkite UI.

Once the PR is approved and ready to go, please make sure to run full CI as it is required to merge (or just use auto-merge).

To run full CI, you can do one of these:

• Comment /ready on the PR
• Add ready label to the PR
• Enable auto-merge.

🚀

[jeejeelee]

/ready

[jeejeelee]

https://buildkite.com/vllm/ci-aws/builds/6547# can be used as a comparison

[jeejeelee]

@simon-mo Could you please merge this PR?