Simplify Function class

[ricardoV94]

Description

As discussed in #222 Function is quite bloated.

Some things we could probably remove because nobody uses them:

1. Default values for function arguments
2. output_subset kwarg at call_time

trust_input is useful for speedier evaluations, this should be an explicit kwarg to pytensorf.function and not just a hidden property that power-users know how to change after the function is created