[Frontend][OpenMP] Remove reduction from allowed clauses for target

The "reduction" clause is not allowed on the "target" construct.

Author: kparzysz

llvm/include/llvm/Frontend/OpenMP/OMP.td

@@ -682,7 +682,6 @@ def OMP_Target : Directive<"target"> {
     VersionedClause<OMPC_FirstPrivate>,
     VersionedClause<OMPC_IsDevicePtr>,
     VersionedClause<OMPC_HasDeviceAddr, 51>,
-    VersionedClause<OMPC_Reduction>,
     VersionedClause<OMPC_InReduction, 50>,
     VersionedClause<OMPC_Allocate>,
     VersionedClause<OMPC_UsesAllocators, 50>,