Namespace doesn't need to be followed by semicolon

Summary:
Auto-generated with
```
fbgs "}; // namespace" -l | sort | uniq | sed 's/fbsource.//' | xargs -n 50 sed -i 's_}; // namespace_} // namespace_'
```

Reviewed By: dmm-fb

Differential Revision: D51029740

fbshipit-source-id: 177e3f6e6b0ab7e986b1147952cd5e2f59d4b1fc