[clang] [clang] remove ClassScopeFunctionSpecializationDecl (PR #66636)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

The changes should definitely have a release note so that downstreams can be aware of the changes. This isn't really a potentially breaking change, but we should alert clang-vendors in case a downstream actually cares.

https://github.com/llvm/llvm-project/pull/66636