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

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

> `indvars`, `require<scalar-evolution>`, `nary-reassociate` are still fast on the IR in https://reviews.llvm.org/D3127, https://bugs.llvm.org/show_bug.cgi?id=18606, https://bugs.llvm.org/show_bug.cgi?id=30257, and https://bugs.llvm.org/show_bug.cgi?id=28721

@nikic is this sufficient enough to proceed?

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