Disable standalone relocation packer

We only support relocation packing inside lld now, remove calls to
the standalone relocation packer.  Any shared library built with
LOCAL_USE_CLANG_LLD := false will no longer have relocation packing.

This will also prevent relocation packing on prebuilt shared
libraries.

Also enables relocation packing on Darwin since lld will work on
Darwin.

Bug: 110715614
Test: m checkbuild
Change-Id: Ib4d4bc86f164d05dd78455c8e7605d4b4f5a2a77