[llvm] [DA] remove constraint propagation and coupled/separable subscripts (PR #160924)

[Sebastian Pop via llvm-commits]

sebpop wrote:

> I can share the potentially problematic parts I've noticed, if that would be helpful.

Yes, please.  Make those comments in bug reports: it can be as short as "function() has those lines of code that seem to be wrong in version <sha_key> at <line_numbers>" and we will work on fixing those.

https://github.com/llvm/llvm-project/pull/160924