Fix PLAIN_OUTPUT for normal execution

[Pwuts]

Background

PLAIN_OUTPUT only works when combined with a monkeypatch applied by a pytest fixture.

Changes

• Remove the patch_emit fixture
• Patch the output handler in Logger when config.plain_output is True

Documentation

x

Test Plan

• Tested manually
• CI

PR Quality Checklist

• My pull request is atomic and focuses on a single change.
• I have thoroughly tested my changes with multiple different prompts.
• I have considered potential risks and mitigations for my changes.
• I have documented my changes clearly and comprehensively.
• I have not snuck in any "extra" small tweaks changes.
• I have run the following commands against my code to ensure it passes our linters:

  black .
  isort .
  mypy
  autoflake --remove-all-unused-imports --recursive --ignore-init-module-imports --ignore-pass-after-docstring autogpt tests --in-place

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