[NNC] Remove VarBinding and go back to Let stmts (#42634)
Summary:
Awhile back when commonizing the Let and LetStmt nodes, I ended up removing both and adding a separate VarBinding section the Block. At the time I couldn't find a counter example, but I found it today: Local Vars and Allocations dependencies may go in either direction and so we need to support interleaving of those statements.
So, I've removed all the VarBinding logic and reimplemented Let statements. ZolotukhinM I think you get to say "I told you so". No new tests, existing tests should cover this.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42634
Reviewed By: mruberry
Differential Revision: D22969771
Pulled By: nickgg
fbshipit-source-id: a46c5193357902d0f59bf30ab103fe123b1503f1
