[llvm] [SCEV] Remove EqCacheSCEV (PR #133186)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

> Would #101022 also fix your issue (the PR needs a rebase tho).
Something along those lines would also fix this (also `CompareSCEVComplexity` isn't actually checking if the `std::optional` contains a value in that PR). But removing the cache altogether seems like a cleaner fix. Do you prefer that fix over this one?
> 
> And no, I don't believe that the complexity logic is correctness relevant -- so I'm not sure this is really the root cause of the miscompile you're seeing?
It's quite possible that this is not fixing a miscompile since it's very hard for us to reproduce the miscompile, any change seems to make it go away. But at least this fixes the comparator.

https://github.com/llvm/llvm-project/pull/133186