Let lowerToLoopsUsingSCFForOp delete target op.

The function mlir::scf::lowerToLoopsUsingSCFForOp was not deleting its
(structured) target op, resulting in IR with the expected loop nest in
front of the still remaining (structured) op, e.g. a linalg.matmul.

Author: lhunloh

mlir/lib/Dialect/SCF/Transforms/TileUsingInterface.cpp

@@ -1133,5 +1133,6 @@ mlir::scf::lowerToLoopsUsingSCFForOp(RewriterBase &rewriter,
   if (failed(op.generateScalarImplementation(rewriter, op.getLoc(), ivs))) {
     return failure();
   }
+  rewriter.eraseOp(op);
   return loops;
 }