Revert "[OpenMP][FIX] Explicit barriers in SPMD mode are not aligned"

This seems to be the root cause of hangs on amdgpu. Reverting while investigating.
This reverts commit 7b9844cc8d.

openmp/libomptarget/DeviceRTL/src/Synchronization.cpp

@@ -336,6 +336,9 @@ void __kmpc_barrier(IdentTy *Loc, int32_t TId) {
   if (mapping::isMainThreadInGenericMode())
     return __kmpc_flush(Loc);
 
+  if (mapping::isSPMDMode())
+    return __kmpc_barrier_simple_spmd(Loc, TId);
+
   impl::namedBarrier();
 }