[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

llvm-svn: 365963
GitOrigin-RevId: e4b4f994d2f6a090694276b40d433dc1a58beb24
63 files changed