Fix removal of nodes ingested by multiple downstream nodes

[jmduarte]

• Currently, when a node is removed (such as a linear activation), it is only replaced correctly in the first downstream node that uses it
• This PR replaces it in all downstream nodes

To do

• Add a pytest

@nickshey

[thesps]

Can we get a new pytest for this?

This seems all good when the prev_node itself has a single output that is consumed multiple times, but brings us a bit closer to needing to deal with a prev_node that has multiple outputs (I think only Clone has that right now) since we always reconnect to prev_node.outputs[0].

Edit: I pushed the branch to local pr/544 to trigger pytests CI. The failing tests are unrelated to this PR.