[clang][dataflow] Remove checks that test for consistency between...

[clang][dataflow] Remove checks that test for consistency between `StructValue` and `AggregateStorageLocation`.

Now that the redundancy between these two classes has been eliminated, these
checks aren't needed any more.

Reviewed By: ymandel, xazax.hun

Differential Revision: https://reviews.llvm.org/D155813