feat!: remove deprecated signal parameter from consumer

[navinkarkera]

Description: Removes deprecated signal parameter and bumps openedx-events to 8.0.0

Dependencies:

• Remove signal parameter from consumer openedx-events#218

Merge deadline: List merge deadline (if any)

Reviewers:

• @bmtcril

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

Post merge:

• Create a tag
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)

[openedx-webhooks]

Thanks for the pull request, @navinkarkera! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

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Please let us know once your PR is ready for our review and all tests are green.

[openedx-webhooks]

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