chore: remove hermetic build toolset and workflow for new library (googleapis#13597)

Remove the `generate_new_client_hermetic_build.yaml` workflow and its
associated scripts in `generation/new_client_hermetic_build`. This
tooling is outdated as new libraries are now onboarded using Librarian,
see more at
[DEVELOPMENT.md](https://github.com/googleapis/google-cloud-java/blob/main/DEVELOPMENT.md#3-code-generation-librarian).


Fixes googleapis/librarian#5239

Author: zhumin8