- Fix unused parameter warning in StlVectorTest.cpp
- Fix unused parameter warning in StlVectorTest.cpp

Summary: We are going to enable `-Werror=unused-parameter` flag and I need to manually fix some files so we rest of this process can be automated with a tool called clang-tidy.

Reviewed By: yfeldblum

Differential Revision: D7071617

fbshipit-source-id: 0165d9c79834b479ad0f598ea64404a86f47dcc6

facebook/folly,facebook/folly,rklabs/folly,rklabs/folly,rklabs/folly,facebook/folly,facebook/folly,rklabs/folly,rklabs/folly,facebook/folly