Remove type visibility specifiers from new chrono types.

_LIBCPP_TYPE_VIS is only really needed on types with a vtable.
And on Windows it doesn't work with types that have only inline methods.

This patch removes the unneeded attributes.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356637 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed