fix the docstring of `RandomSampler` (#19113)
Summary:
fix
- the order of `Arguments` in `RandomSampler` doc
- the meaningless check of `replacement`'s type.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19113
Differential Revision: D15013081
Pulled By: ezyang
fbshipit-source-id: 39e367f42841de6814b1214eb9df7b75f14f747e
