[clang] [clang][ASTImporter] Remove 'hasReturnTypeDeclaredInside' (PR #169504)

[Balázs Kéri via cfe-commits]

balazske wrote:

I have checked some projects (with no CTU crashes before the fix) and did not found new problems after this change.

https://github.com/llvm/llvm-project/pull/169504