Revert "[OpenMP] [OMPIRBuilder] Create a new datatype to hold the unique target region info"

This reverts commit 3d0e9edd.

Breaking HWASAN buildbot:
https://lab.llvm.org/buildbot/#/builders/236/builds/786

Shown by targetted builds breaking at this patch:
Built at this patch: https://lab.llvm.org/buildbot/#/builders/236/builds/803
Built at prior patch: https://lab.llvm.org/buildbot/#/builders/236/builds/804