[tests] remove pile-val-backup dataset from tests

[brian-dellabetta]

SUMMARY:
This PR

• Removes pile-val-dataset from e2e tests, as it is no longer used in examples and the processing logic was flawed
• Fixes a model validation error introduced in [Multi-modifier] Support scoped application of quantization config/status #1772 that was preventing AWQModifier from running one of the validations, causing it to be in an invalid state (AWQModifier.validate_model_after was preventing QuantizationMixin.validate_model_after from running). With these changes, tests pass and the compressed model generates meaningful responses. It was previously generating all 0s

TEST PLAN:
CADENCE=nightly TEST_DATA_FILE=tests/e2e/vLLM/configs/w4a16_grouped_quant_sym_awq.yaml pytest -s tests/e2e/vLLM/test_vllm.py and
CADENCE=nightly TEST_DATA_FILE=tests/e2e/vLLM/configs/w4a16_grouped_quant_asym_awq.yaml pytest -s tests/e2e/vLLM/test_vllm.py
both pass with output like

PROMPT:
The capital of France is
GENERATED TEXT:
 Paris, which is also the country's largest city.

PROMPT:
The president of the US is
GENERATED TEXT:
 named, but the name of the Vice President is not given. In the case

PROMPT:
My name is
GENERATED TEXT:
 Emily and I am from Canada. I have always been fascinated with

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[fynnsu]

Looks good!

My only comment is maybe we should change the name of
tests/e2e/vLLM/recipes/WNA16/recipe_w4a16_group_quant_asym_awq.yaml
to match
tests/e2e/vLLM/recipes/WNA16/recipe_w4a16_awq_sym.yaml if we're just directly using the W4A16_ASYM scheme. But also fine as is.

[shanjiaz]

Looks good to me! Thanks for fixing!