ci: remove obsolete Cloud Build trigger build-library-generation-image-monorepo (java-hermetic-build-prod) #14869

Description

Every commit pushed to main triggers the build-library-generation-image-monorepo (java-hermetic-build-prod) Cloud Build check, which immediately fails with:

File sdk-platform-java/.cloudbuild/library_generation/cloudbuild-library-generation-push.yaml not found

Cause

PR #13616 (5590509adde278dcf334c61af94a298429942d2c) removed the obsolete hermetic build workflows and sdk-platform-java/.cloudbuild/library_generation/ after migrating to Librarian, but the corresponding Cloud Build trigger in GCP project java-hermetic-build-prod (122457793624, region us-central1) is still enabled.

Example Failure

• Check run: https://github.com/googleapis/google-cloud-java/runs/122414069145

Proposed Fix

Disable or delete the build-library-generation-image-monorepo Cloud Build trigger in the java-hermetic-build-prod project.