[easy] Pass compile_fx only the config patches

Previously we were passing compile_fx the entire default inductor config
with the patches applied to it.

compile_fx only needs to be passed the patches (reference:
https://github.com/pytorch/pytorch/blob/29317f8585ecb232412df3f39734490f0f6d8230/torch/_inductor/compile_fx.py#L1873-L1880)

This PR changes vLLM to only pass the patches. This makes debugging
things easier (I can stare at just the delta and see what vLLM changed).

Test Plan:
I ran the following command and verified that performance didn't change.
```
VLLM_USE_V1=1 python benchmark_latency.py --model meta-llama/Meta-Llama-3-8B --batch-size 1 -O '{"level": 3, "compile_sizes": {1, 2}}'
```

Signed-off-by: rzou <zou3519@gmail.com>

Author: zou3519

vllm/compilation/compiler_interface.py

@@ -167,8 +167,7 @@ def compile(
         compiler_config: Dict[str, Any],
         runtime_shape: Optional[int] = None
     ) -> Tuple[Optional[Callable], Optional[Any]]:
-        from torch._inductor import config
-        current_config = config.get_config_copy()
+        current_config = {}
         from torch._inductor.compile_fx import compile_fx
 
         # disable remote cache