Revert "Establish the <bit> header. NFC yet. Reviewed as https://reviews.llvm.org/D50815"

Breaks build on sanitizer bots.

This reverts commit r339943.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@339971 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed