[OpenMP][NFC] Do not collect kernels if they are not used (#135252)

Author: jdoerfert

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

@@ -5856,8 +5856,6 @@ PreservedAnalyses OpenMPOptCGSCCPass::run(LazyCallGraph::SCC &C,
   if (PrintModuleBeforeOptimizations)
     LLVM_DEBUG(dbgs() << TAG << "Module before OpenMPOpt CGSCC Pass:\n" << M);
 
-  KernelSet Kernels = getDeviceKernels(M);
-
   FunctionAnalysisManager &FAM =
       AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();