Clean up unused code creation code related to unsupported providers
Background
With code suggestions being only served from google models, and code generations from anthropic models, do you agree that it would make sense to remove dead code related to unsupported provides, like code generation prompt for code-bison, or code completion prompt for anthropic. Despite removing code related to unsupported providers we still want to leave abstraction that supports selection of different providers, since that feature might be reintroduced in the upcoming feature
Goal
Remove following unused files and corresponding tests: