Remove cudnn conv in unittest, test=develop (#26489)

Remove cudnn conv in Unittest because the cudnn conv, which is assigned to OP owner, hasn't been fixed.

python/paddle/fluid/tests/unittests/seresnext_net.py

@@ -36,7 +36,7 @@ remove_dropout = False
 # and Executor is different.
 remove_bn = False
 
-remove_cudnn_conv = False
+remove_cudnn_conv = True
 
 remove_dropout = True
 remove_bn = True