[ELF] Always separate relative relocations regardless of -z combreloc (#187964)
Remove the combreloc guard from addReloc and mergeRels so that
relative relocations are always routed to relativeRelocs, even with -z
nocombreloc or --pack-dyn-relocs=android.
Update AndroidPackedRelocationSection::updateAllocSize to iterate
both relativeRelocs and relocs.