[mlir] cleanup transform payload setting

[ftynse]

Summary

Before the multi-handle relaxation, the transform interpreter did not
actually set payload for a handle that had no further uses as a hacky
mechanism to work around the multi-handle problem. This is no longer
necessary and can be removed to avoid debugging surprises when a handle
has no payload even when its producing op assigned it.

[ftynse]

Rebase.

mlir/lib/Dialect/Transform/IR/TransformInterfaces.cpp

 }
 
 LogicalResult
 transform::TransformState::setPayloadOps(Value value,
                                          ArrayRef<Operation *> targets) {
   assert(value != kTopLevelValue &&
          "attempting to reset the transformation root");
 
-  // TODO: this may go now
-  if (value.use_empty())
-    return success();
-
   auto iface = value.getType().cast<TransformTypeInterface>();
   DiagnosedSilenceableFailure result =
       iface.checkPayload(value.getLoc(), targets);
   if (failed(result.checkAndReport()))
     return failure();
 
   // Setting new payload for the value without cleaning it first is a misuse of
   // the API, assert here.