chore: remove all explicit transport options

[jskeet]

This does not create any differences after regeneration (because the options are all inferred correctly).

[gemini-code-assist]

Code Review

This pull request removes explicit transport configuration settings for numerous Google Cloud APIs within the librarian.yaml file. The review feedback suggests that these changes introduce fragility into the build process by relying on the generator's inference logic rather than explicit definitions. This is particularly concerning for APIs with specific transport requirements, such as those that are REST-only or gRPC-only, and maintaining these explicit settings is recommended for robustness and clarity.

[gemini-code-assist]

While the goal of reducing configuration is understandable, removing explicit transport settings across the file makes the build process more fragile. It relies on the generator's ability to correctly infer the transport for each of the many API versions.

This is particularly risky for APIs with non-standard transports, for example:

• google/cloud/compute/v1 which is rest-only (line 1361).
• Several beta versions which are grpc-only, while their v1 counterparts are grpc+rest (e.g., line 996).

If the generator's inference logic changes in the future, it could silently introduce incorrect transport support. Explicitly defining the transport is more robust and self-documenting. It is recommended to revert these changes to maintain explicitness and reduce future maintenance risks.