[libcxx] [test] Remove asserts that <cstddef> and <stdexcept> are included by <bitset>

Reviewed as https://reviews.llvm.org/D50421

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@339212 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed