elf: Remove fallback to the start of DT_STRTAB for dladdr

elf: Remove fallback to the start of DT_STRTAB for dladdr

When neither DT_HASH nor DT_GNU_HASH is present, the code scans
[DT_SYMTAB, DT_STRTAB). However, there is no guarantee that .dynstr
immediately follows .dynsym (e.g. lld typically places .gnu.version
after .dynsym).

In the absence of a hash table, symbol lookup will always fail
(map->l_nbuckets == 0 in dl-lookup.c) as if the object has no symbol, so
it seems fair for dladdr to do the same.

Reviewed-by: Florian Weimer <fweimer@redhat.com>