Revert "[DataFormatters] Add formatter for C++17 std::variant"

This reverts commit r342421.

Because it breaks build bot http://green.lab.llvm.org/green/job/lldb-cmake-clang-5.0.2//418/console

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@342424 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed