Multi output fix 2

[calad0i]

Description

Fixes the following:

• Fix output node updating mechanism. The current parser assumes set(outputs)-set(inputs) are the output nodes, which is not true if some intermediate nodes are being outputted, or if any inputs are unused.
• remove_node is updated to correctly rewire in all cases, including leaf/intermediate+leaf nodes. Deprecate arg rewire
• Drop and rewire flatten layers instead of making variable name alias to avoid errors when the tensor is outputted.
• Update flatten layer's output shape in io_stream to correctly handle the case where

Type of change

• Bug fix (non-breaking change that fixes an issue)

Tests

test/pytest/test_multiout_network.py/test_multi_output_nn_2

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.