Remove default inputs dictionary in Truss and Baseten client

Old versus new model invocation syntax

We paid down some technical debt and, in doing so, removed a papercut from the Baseten and Truss developer experience.

It used to be that all model invocations had to be formatted as:

    "inputs": $MODEL_INPUT

We cleaned up the model packaging templates in Truss so that you can invoke your model on any JSON-serializable input. Now, pass your lists, strings, numbers, and more directly to your model. In other words, now you can simply call your model with $MODEL_INPUT.

This change only affects newly created model versions that use truss > 0.4.0 and baseten > 0.5.0, so your invocations of existing models won’t break. And you can always edit the predict() and preprocess() functions in your Truss’ to change your model input format.