[llvm] [SCEVExpander] Fix addrec cost model (PR #106704)

[Philip Reames via llvm-commits]

preames wrote:

> Did we maybe duplicate some code in SCEVExpander which we shouldn't have?

There does look like there's some code at the bottom of visitAddRecExpr which tried to handle non-afffine addrecs with something close to this costing.  I think that code is simply dead though, and can be replaced with an assert.  

https://github.com/llvm/llvm-project/pull/106704