revert openai agents sdk temp fix

[bbqiu]

reverting #342 now that mlflow/mlflow#21038 is released

manually tested

running the following file generates the results below in the two diff cases:

import databricks_openai
import mlflow
import os

os.environ["DATABRICKS_CONFIG_PROFILE"] = "dogfood"
mlflow.set_tracking_uri("databricks")
mlflow.set_experiment(experiment_id="1981078730603410")

# mlflow.openai.autolog(disable_openai_agent_tracer=False)
mlflow.openai.autolog()

client = databricks_openai.DatabricksOpenAI()

response = client.chat.completions.create(
    model="databricks-gpt-5",
    messages=[{"role": "user", "content": "What is the capital of France?"}],
)

print(response)

Results confirm everything:
  ┌───────────────────┬─────────────────────┬──────────────────────────────────────────────────────────────────────┐
  │ databricks-openai │       mlflow        │                                Result                                │
  ├───────────────────┼─────────────────────┼──────────────────────────────────────────────────────────────────────┤
  │ 0.12.0            │ 3.10.1 (with fix)   │ Works                                                                │
  ├───────────────────┼─────────────────────┼──────────────────────────────────────────────────────────────────────┤
  │ 0.12.0            │ 3.10.0 (without     │ AttributeError: 'NoneType' object has no attribute                   │
  │                   │ fix)                │ '_multi_processor'                                                   │
  └───────────────────┴─────────────────────┴──────────────────────────────────────────────────────────────────────┘```