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

[Sebastian Pop via llvm-commits]

sebpop wrote:

> I was going to suggest that putting it under an option would be the polite thing to do.

I agree, however the amount of code constraint propagation needs under the current implementation is ~2000 SLoC which is half the size of the rest of DA.  

Constraint propagation simplifies the MIV test based on info inferred from SIV tests.
See Section 5.3 in https://softlib.rice.edu/pub/CRPC-TRs/reports/CRPC-TR90103-S.pdf and the running example:
```
for i
  for j
    A(i+1, i+j) = A(i, i+j)
```
Where the first SIV subscript `i0+1` vs. `i1` gets distance `-1` propagated into the second MIV subscript `i0+j0` vs. `i1+j1` that then becomes SIV under the new constraints "j0 - 1" vs. "j1" which solves faster than the original MIV test.



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