[OpenMP] Remove OMP spec versioning Remove all older OMP spec versioning from the runtime and build system. Patch by Terry Wilmarth Differential Revision: https://reviews.llvm.org/D64534 git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@365963 91177308-0d34-0410-b5e6-96231b3b80d8