clean_duplicate_history uses default model manager, which may filter out relevant instances

[JackAtOmenApps]

Describe the bug
When using clean_duplicate_history, and models with a default manager (objects = XYZ) which filters out model instances may fail to correctly de-duplicate history (because it can't see all of the instances).

This is very similar to issue #703 for bulk_update_with_history (and its fix, #709).

To Reproduce
Steps to reproduce the behavior:

1. Install django-simple-history
2. Add a model manager which applies filtering to a model which uses django-simple-history
3. Run clean_duplicate_history --auto
4. De-duplication of the model may be incomplete or not perform any work at all

Expected behavior
clean_duplicate_history should use Django's base manager to ensure all model instances are checked for duplicates.

Note: #804 is the potential fix for this issue

[ddabble]

Closing, now that #1115 (replacing #804) was merged.