chore: remove deprecated api_helpers module and the deprecated body attrs

[kgriffs]

Summary of Changes

Removed deprecated api helpers module and body attibutes.

Related Issues

Supersedes #1986

Pull Request Checklist

This is just a reminder about the most common mistakes. Please make sure that you tick all appropriate boxes. But please read our contribution guide at least once; it will save you a few review cycles!

If an item doesn't apply to your pull request, check it anyway to make it apparent that there's nothing to do.

• [x] Applied changes to both WSGI and ASGI code paths and interfaces (where applicable).
• [x] Added tests for changed code.
• [x] Prefixed code comments with GitHub nick and an appropriate prefix.
• [x] Coding style is consistent with the rest of the framework.
• [x] Updated documentation for changed code.
  • [x] Added docstrings for any new classes, functions, or modules.
  • [x] Updated docstrings for any modifications to existing code.
  • [x] Updated both WSGI and ASGI docs (where applicable).
  • [x] Added references to new classes, functions, or modules to the relevant RST file under docs/.
  • [x] Updated all relevant supporting documentation files under docs/.
  • [x] A copyright notice is included at the top of any new modules (using your own name or the name of your organization).
  • [x] Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
• [x] Changes (and possible deprecations) have towncrier news fragments under docs/_newsfragments/, with the file name format {issue_number}.{fragment_type}.rst. (Run towncrier --draft to ensure it renders correctly.)

If you have any questions to any of the points above, just submit and ask! This checklist is here to help you, not to deter you from contributing!

PR template inspired by the attrs project.

[codecov[bot]]

Codecov Report

Merging #2090 (98d37be) into master (492087f) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2090   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           63        62    -1     
  Lines         6752      6747    -5     
  Branches      1254      1255    +1     
=========================================
- Hits          6752      6747    -5     

Impacted Files	Coverage Δ
falcon/__init__.py	100.00% <ø> (ø)
falcon/asgi/response.py	100.00% <ø> (ø)
falcon/util/sync.py	100.00% <ø> (ø)
falcon/http_status.py	100.00% <100.00%> (ø)
falcon/response.py	100.00% <100.00%> (ø)
falcon/util/__init__.py	100.00% <100.00%> (ø)
falcon/util/deprecation.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.