[clang] [Clang] Fix 'counted_by' for nested struct pointers (PR #110497)

[Jan Hendrik Farr via cfe-commits]

Cydox wrote:

Removed the special case for DeclRefExpr, as this can also be handled by the pointer case. A few were adjusted, but none of them changed any behavior.

That additional commit is not necessary to fix anything, it's just cleanup.

https://github.com/llvm/llvm-project/pull/110497