[libc++] Remove C++03 variadics in shared_ptr

    Summary: As suggested by @ldionne in D66178, this patch removes C++03 variadics //only//. Following patches will apply more updates.

    Reviewers: ldionne, EricWF, mclow.lists

    Subscribers: christof, dexonsmith, libcxx-commits, ldionne

    Tags: #libc

    Differential Revision: https://reviews.llvm.org/D67675

llvm-svn: 372780