Fully remove ETL_VERSION

[ghukill]

Purpose and background context

Fully remove ETL_VERSION env var from testing.

Includes new or updated dependencies?

NO

Changes expectations for external applications?

NO

What are the relevant tickets?

• None

Developer

• All new ENV is documented in README
• All new ENV has been added to staging and production environments
• All related Jira tickets are linked in commit message(s)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer(s)

• The commit message is clear and follows our guidelines (not just this PR message)
• There are appropriate tests covering any new functionality
• The provided documentation is sufficient for understanding any new functionality introduced
• Any manual tests have been performed and verified
• New dependencies are appropriate or there were no changes