hasDynamicLinker() was just kind of lying in the case of Darwin platforms for
the benefit of std.zig.system.detectAbiAndDynamicLinker(). A better name would
have been hasElfDynamicLinker() or something. It also got the answer wrong for a
bunch of platforms that don't actually use ELF. Anyway, this was clearly the
wrong layer to do this at, so remove this function and instead use
DynamicLinker.kind() + an isDarwin() check in detectAbiAndDynamicLinker().
27c85e5969