fix API transaction DELETE handling to return 404 on non-existing item

[tomkralidis]

Description
Running an API DELETE query on a repository where a given identifier does not exist does not return a 404 (but should).
Steps to Reproduce

• run pygeoapi with a collection that has a provider with transactional capabilities (then setting provider editable: true)
• issue curl -X 'DELETE' \ 'http://localhost:5000/collections/some-collection/items/id-notfound' \ -H 'accept: */*'
  Expected behavior
  API should return 404, not 201.
  Screenshots/Tracebacks
  If applicable, add screenshots to help explain your problem.

Environment

• OS: any
• Python version: 3.12
• pygeoapi version: master

Additional context
Discovered as part of #2220 (review)