chore(asm): remove old django user block mechanism

[christophe-papazian]

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/appsec/trace_utils/__init__.py                                  @DataDog/asm-python
ddtrace/contrib/trace_utils.py                                          @DataDog/apm-core-python @DataDog/apm-idm-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: christophe-papazian/simplify-ATO-blocking
Commit report: 333f4f4
Test service: dd-trace-py

✅ 0 Failed, 130 Passed, 1468 Skipped, 4m 10.34s Total duration (35m 42.12s time saved)