[clang] [clang][AST] Stop creating `ConstantExpr` nodes without a result (PR #229761)

[Timm Baeder via cfe-commits]

tbaederr wrote:

I've removed the assertion but there's still the question if it should be _possible_ to create a `ConstantExpr` without a result, i.e. if `ConstantResultStorageKind::None` should exist at all. We do check for it in a couple of places but never use it.

https://github.com/llvm/llvm-project/pull/229761