[llvm-c] Remove dead typedef

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194379 91177308-0d34-0410-b5e6-96231b3b80d8
[OCaml] Make Llvm_target.DataLayout.t automatically managed

This breaks the API by removing Llvm_target.DataLayout.dispose.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194380 91177308-0d34-0410-b5e6-96231b3b80d8