UML-3109 Remove build_admin feature flag from TF

[ntse]

Purpose

Simplify the Terraform case by removing a now unnecessary ternary.

Fixes UML-3109

Approach

Remove the build_admin flag as it exists in all environments. Use moved resources to refactor the code.

Learning

Any tips and tricks, blog posts or tools which helped you. Plus anything notable you've discovered about the Use a Lasting Power of Attorney service

Checklist

• I have performed a self-review of my own code
• I have added relevant logging with appropriate levels to my code
• New event_codes have been documented on the wiki page
• I have updated documentation (Confluence/GitHub wiki/tech debt doc) where relevant
• I have added tests to prove my work
• I have added welsh translation tags and updated translation files
• I have run an accessibility tool on any pages I have made changes to and fixed any issues found
• I have notified the Interaction Designer of any content changes so that appropriate screenshots/flow diagram changes can be made
• The product team have tested these changes