refactor: remove unnecessary _completed_process attribute storage

- Remove _completed_process field from EntrypointOutput class
- No functionality lost as the attribute was never used after assignment
- Simplifies the class by not storing unnecessary references
- Addresses GitHub PR feedback from @aaronsteers

Co-Authored-By: AJ Steers <[email protected]>

Author: devin-ai-integration[bot]

airbyte_cdk/test/entrypoint_wrapper.py

@@ -77,7 +77,6 @@ def __init__(
 
         self._messages: list[AirbyteMessage] | None = None
         self._message_file: Path | None = message_file
-        self._completed_process: Optional[subprocess.CompletedProcess[str]] = None
         if messages:
             try:
                 self._messages = [self._parse_message(message) for message in messages]
@@ -309,7 +308,6 @@ def from_completed_process(
         else:
             instance = cls()
 
-        instance._completed_process = completed_process
         return instance