[sanitizer] Remove spurious semi-colon

Summary:
An extra ';' at the end of a namespace triggers a pedantic warning:
```
.../sanitizer_common/sanitizer_type_traits.h:42:2: warning: extra ‘;’ [-Wpedantic]
 };  // namespace __sanitizer
```

Reviewers: eugenis, delcypher

Reviewed By: eugenis

Subscribers: kubamracek, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D55849

llvm-svn: 349666