[Allocator] Remove a really problematic overload. This is very confusing
because there is another (size_t, size_t) overload of Allocator, and the
only distinguishing factor is that one is a tempalte and the other
isn't. There was only one usage of this and that one was easily
converted to carry the alignment constraint in the type itself.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206325 91177308-0d34-0410-b5e6-96231b3b80d8