Retire TSV loading workflow

[AetherUnbound]

Fixes

Fixes WordPress/openverse#1542 by @stacimc

Description

This PR retires the tsv_to_postgres_loader DAG, since it is no longer used in any of our ingestion workflows 🎉 I've also removed some no-obsolete code related to TSV pathing - this is covered by the DAG's XComs in the way our current pipelines are set up.

Testing Instructions

1. just test
2. Run both regular and legacy provider DAG scripts and check that records still make their way into the database (I tried SMK, Brooklyn, and Jamendo)
3. Ensure that the tsv_to_postgres_workflow doesn't show up in your DAGs list locally.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[stacimc]

🎉

Tested Smithsonian and Stocksnap just to be thorough. Great!

[krysal]

LGTM! Tested the WordPress Photo Directory script and it loads rows in the image table 👍

[krysal]

I was about to ask if we don't need to conserve this documentation but I see we have it where it was moved :)

openverse-catalog/openverse_catalog/dags/database/loader_workflow.py

Lines 2 to 6 in 3217ed5

	#### Database Loader DAG
	**DB Loader Apache Airflow DAG** (directed acyclic graph) takes the media data saved
	locally in TSV files, cleans it using an intermediate database table, and saves
	the cleaned-up data into the main database (also called upstream or Openledger).

[AetherUnbound]

I made sure to check that as well 😄 Should have made a note in the description, apologies!