[mlir][NFC] Remove unused variable 'indexType' in GPUTransformOps.cpp

/data/jiefu/llvm-project/mlir/lib/Dialect/GPU/TransformOps/GPUTransformOps.cpp:430:13: error: unused variable 'indexType' [-Werror,-Wunused-variable]
  IndexType indexType = rewriter.getIndexType();
            ^
1 error generated.

mlir/lib/Dialect/GPU/TransformOps/GPUTransformOps.cpp

@@ -427,7 +427,6 @@ static DiagnosedSilenceableFailure rewriteOneForeachThreadToGpuThreads(
 
   // Step 3. Create the gpu.thread ops and map the induction variables to the
   // newly created ops.
-  IndexType indexType = rewriter.getIndexType();
   // Replace ids of dimension size 1 by zero to simplify the IR.
   SmallVector<Value> threadOpsUpdated(threadOps.begin(), threadOps.end());
   assert(threadOps.size() == globalBlockDims.size());