[Core][Misc] Clean up ProfileExecuteDuration (#6461)

### What this PR does / why we need it?
This PR removes the custom `ProfileExecuteDuration` utility and its
usages across the codebase. This utility was used for profiling
execution duration of different stages in the inference process. It is
replaced by the standard `vllm.v1.utils.record_function_or_nullcontext`,
which integrates with PyTorch's profiler.

This change simplifies the code by removing a custom implementation in
favor of an upstream utility, improving maintainability. Associated
documentation and tests for `ProfileExecuteDuration` are also removed.

### Does this PR introduce _any_ user-facing change?
`VLLM_ASCEND_MODEL_EXECUTE_TIME_OBSERVE` env is removed now.

### How was this patch tested?
CI passed. The changes are a cleanup and replacement with a standard
utility. Existing tests cover the functionality. The removed feature had
its own tests which are also removed.

Related RFC: #5304

- vLLM version: v0.14.1
- vLLM main:
dc917cceb8

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

vllm_ascend/envs.py

@@ -60,11 +60,6 @@ env_variables: dict[str, Callable[[], Any]] = {
     # In this case, developers need to set this value to "0.9.0" to make sure
     # that the correct package is installed.
     "VLLM_VERSION": lambda: os.getenv("VLLM_VERSION", None),
-    # Whether to enable the model execute time observe profile. Disable it when
-    # running vllm ascend in production environment.
-    "VLLM_ASCEND_MODEL_EXECUTE_TIME_OBSERVE": lambda: bool(
-        int(os.getenv("VLLM_ASCEND_MODEL_EXECUTE_TIME_OBSERVE", "0"))
-    ),
     # Some models are optimized by vllm ascend. While in some case, e.g. rlhf
     # training, the optimized model may not be suitable. In this case, set this
     # value to False to disable the optimized model.