fix: Remove unused application_record.rb file

Removed app/models/application_record.rb since it references
ActiveRecord::Base which is not loaded in this application.
This application uses Couchbase SDK directly with the
CouchbaseConnection module, not ActiveRecord.

This fixes the CI error:
NameError: uninitialized constant ActiveRecord

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: teetangh