[clang-tools-extra] [clang] remove ClassScopeFunctionSpecializationDecl (PR #66636)

[Erich Keane via cfe-commits]

erichkeane wrote:

I don't have any comments, though someone with knowledge of teh clang-tools-extra stuff would be nice to take a look, as well as someone familiar with the serialization.  @AaronBallman .

ALSO, this might need a release note and does this need to be mailed to the 'breaking changes' vendor list since it is significantly going to change the AST?

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