linker: cleanup of undefined state handling, which is really dead code

Given that _elf_lookup (and thus, _do_lookup) cannot possibly return an
undefined symbol (due to the check for SHN_UNDEF in _elf_lookup), there's
no need for spurious checks for SHN_UNDEF on its return value.

Conflicts:

	linker/linker.c

Change-Id: Ic73cf439924b45f72d4d9ba3f64a888c96cbbd9b

linker/linker.c

@@ -462,7 +462,7 @@ soinfo_do_lookup(soinfo *si, const char *name, Elf32_Addr *offset)
             DEBUG("%5d %s: looking up %s in %s\n",
                   pid, si->name, name, lsi->name);
             s = soinfo_elf_lookup(lsi, elf_hash, name);
-            if ((s != NULL) && (s->st_shndx != SHN_UNDEF))
+            if (s != NULL)
                 goto done;
         }
     }