[CMake] Remove legacy LIBOMP_LIT_ARGS
[CMake] Remove legacy LIBOMP_LIT_ARGS

The bots have been updated, this option isn't needed anymore.

git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@320153 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp