mxnet.random.seed docs error

## Description
Sphinx throws an error when generating the docs for this function.

## Error
```
/home/ubuntu/incubator-mxnet/python/mxnet/random.py:docstring of mxnet.random.seed:0: WARNING: duplicate object description of mxnet.random.seed, other instance in /home/ubuntu/incubator-mxnet/docs/api/python/ndarray/ndarray.md, use :noindex: for one of them

```