Delete nested .github/workflows/ci.yml files from api/ and receiptwitness/
directories. These workflows were from the polyrepo era and reference the
deleted cartsnitch/common repo. They do not execute as GitHub Actions (not
at repo root) and are confusing.
No functional change — the monorepo CI is defined at .github/workflows/.
Co-Authored-By: Paperclip <noreply@paperclip.ing>