[llvm] [NFC][LLVM] Namespace cleanup in ScalarEvolution (PR #166620)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata commented:

The `ScalarEvolutionDivision.cpp` bits look good.  I'm not sure about the `ScalarEvolution.cpp` bits.  I generally like clean code, but if we have to add a comment to accomplish the cleanup task, we might be increasing cognitive load.  The reader would have to understand the code itself and why the code is written in a particular manner.

https://github.com/llvm/llvm-project/pull/166620