Remove pw_ehr_cta_drupal_source_of_truth flipper

[jilladams]

Description

The flipper pw_ehr_cta_drupal_source_of_truth was created during converting Cerner to use KISS data ( #8198 epic).

When the work in that epic is complete, we need to set the FE logic to always-on regardless of this flipper, and remove the flipper itself.

Additional Information

This ticket is in an epic where we did work with KISS. There are remaining open tickets; can an FE person please look at the other open tickets to see if there are any repercussions to removing this.

ACs

• [ ] In FE code (vets-website) update logic to always use the route that's used when flipper is on, regardless of flipper state
• [ ] In vets-api, deprecate the pw_ehr_cta_drupal_source_of_truth flipper
• [ ] Open a Platform support request to manually update the Flipper dashboard to remove that flipper, e.g. https://dsva.slack.com/archives/CBU0KDSB1/p1706215548005939

[jilladams]

We need to understand before working this ticket whether removing the flipper will affect our ability to complete the remainder of the KISS-related tickets.

[FranECross]

Will refine and have in Stretch/Next Sprint if someone can get to it; not urgent at all.