[clang] [clang codegen][NFC] Delete dead code in constant emission. (PR #90106)

[John McCall via cfe-commits]

https://github.com/rjmccall commented:

The Apple fork does actually use this downstream (for address-sensitive `__ptrauth`), and we've recently (finally) been making progress in upstreaming that work.  Obviously, we could delete it and then reinstate it when we catch up to this point in upstreaming, but I don't think it's actively harmful to keep around in the short term.

https://github.com/llvm/llvm-project/pull/90106