[llvm] Delete the incorrect assert that assumes size of `APFloat` is the same as `IEEEFloat`. (PR #111780)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> > not all the members of APFloat is IEEE.
> 
> Oh I see. Do you add a new impl whose size is larger than `detail::IEEEFloat`?

If so, at least we can assert `sizeof(APFloat) == sizeof(APFloat::Storage)`.


https://github.com/llvm/llvm-project/pull/111780