- 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

folly/test/stl_tests/StlVectorTest.cpp

@@ -2012,6 +2012,7 @@ STL_TEST("23.2.1 Table 99.5", copyWithAllocator, is_copy_constructible, a, m) {
 
 STL_TEST("23.2.1 Table 99.6", moveConstructionWithAllocator,
          is_destructible, a) {
+  (void)a;
   // there is nothing new to test here
 }