Clean up existing indices on Upload (aka ReportSession)

[Swatinem]

This in particular cleans up the existing indices that exist in the production DB but not in django:

We drop these indices for the following reasons:

• upload_index_id_type_number: This matches the above state migration,
  and it looks like the index does not actually exist in the production DB.

The following indices exist in the production DB, but not in django state/migrations:

• reports_upload_order_number_idx:
  We never query by the order_number alone, so this index is likely unused.
• reports_upload_report_id_f6b4ffae: Queries on report_id should already been covered by the
  newly added index on report_id+upload_type.
• reports_upload_report_id_upload_type_index_ccnew:
  This seems to be a manually added variant of the upload_report_type_idx index and is thus duplicated.
• reports_upload_report_id_upload_type_order_number_index:
  This is the same as the above, except with an additional order_number.
  We do use it in queries, but I doubt the index pulls its weight, as the order_number changes quite
  frequently so the index is costly to maintain.

[Swatinem]

Looks like the created_at index might be used only for this query here:
https://github.com/codecov/worker/blob/ad3621cbee3619ec1b47ee55a1050e8be4343dda/tasks/brolly_stats_rollup.py#L53

But for that case, I believe having an index would make sense, as otherwise it would do a full table scan there :-D

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.97%. Comparing base (99581a7) to head (610dd21).

❗ Current head 610dd21 differs from pull request most recent head ad1607c

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #442      +/-   ##
==========================================
- Coverage   90.55%   89.97%   -0.58%     
==========================================
  Files         404      324      -80     
  Lines       12562     9199    -3363     
  Branches     2107     1633     -474     
==========================================
- Hits        11375     8277    -3098     
+ Misses       1078      859     -219     
+ Partials      109       63      -46     

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[Swatinem]

I updated the PR to add a bunch more manually added indices to the cleanup, and after running this, the state of the production DB should be fully aligned with the django migration state.