Draft: Remove old encrypted token implementation - part 2

What does this MR do and why?

This MR removes the feature flag for encrypted trigger tokens and ignores the old token column. It also removes the old and never used encrypted_token and encrypted_token_iv columns. Since the migration for column token gets finalized in 18.6, this should be merged in 18.7.

Changelog: changed

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #554239