ContainerRegistry: Remove return-type overloaded client functions

[euanh]

Motivation

Return type overloads can be puzzling for new readers because the same function call returns a different type depending on where it is called. In some cases a type annotation is needed at the call site, but when the overloaded function is the final call in another function the compiler can infer the type, so the reader needs to know to check the type of the enclosing function.

In addition, in a future pull request we will need access to the underlying data returned by the HTTP client, in order to verify digests and create ContentDescriptor objects. This refactoring starts to prepare for that and makes the code easier to understand.

Modifications

• Remove return-type overloaded version of executeRequestThrowing()
• Remove return-type overloaded version of getBlob()

Result

Refactoring. No functional change.

Test Plan

Existing tests continue to pass.