Fix the logic for deleting tables on Django 1.7 and higher.
Review Request #10265 — Created Oct. 23, 2018 and submitted
This removes all the custom logic for deleting tables when using Django
1.7 and higher. While this was mostly working fine, there were edge
cases in the implementation, and they became problematic on Django 2.0+.
We now make use of the schema editor's logic to handle all model
deletions, allowing us to benefit from any changes made in Django going
Unit tests pass on Django 1.6 through 1.11. Along with other changes,
they also pass on 2.1.