Remove paddle.metric.auc in 2.0 API (#27851)

python/paddle/metric/__init__.py

@@ -15,11 +15,9 @@
 from .metrics import *
 from . import metrics
 
-from ..fluid.layers.metric_op import auc
 from ..fluid.layers.nn import chunk_eval, mean_iou
 
 __all__ = metrics.__all__ + [
-    'auc',
     'chunk_eval',
     'mean_iou',
 ]