Remove duplicated entries in `random.rst` (#39725)
Summary:
In the current master doc, every function under [`torch.random`](https://pytorch.org/docs/master/random.html) appears twice because the function docs are generated by both `automodule` and `autofunction`.
This PR removes the parts generated by `autofunction`.
See changed docs at https://5751500-65600975-gh.circle-artifacts.com/0/docs/random.html:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39725
Differential Revision: D21983701
Pulled By: ngimel
fbshipit-source-id: 5f515d7fd8034687e754e2c7b2ea9e154b3ea9b9
