Minor refactor in catcache.c

Hi,

```
@@ -1010,7 +1010,7 @@ RehashCatCache(CatCache *cp)
dlist_foreach_modify(iter, &cp->cc_bucket[i])
{
CatCTup *ct = dlist_container(CatCTup, cache_elem, iter.cur);
- int hashIndex = HASH_INDEX(ct->hash_value, newnbuckets);
+ Index hashIndex = HASH_INDEX(ct->hash_value, newnbuckets);

dlist_delete(iter.cur);
dlist_push_head(&newbucket[hashIndex], &ct->cache_elem);
@@ -1048,7 +1048,7 @@ RehashCatCacheLists(CatCache *cp)
dlist_foreach_modify(iter, &cp->cc_lbucket[i])
{
CatCList *cl = dlist_container(CatCList, cache_elem, iter.cur);
- int hashIndex = HASH_INDEX(cl->hash_value, newnbuckets);
+ Index hashIndex = HASH_INDEX(cl->hash_value, newnbuckets);

dlist_delete(iter.cur);
dlist_push_head(&newbucket[hashIndex], &cl->cache_elem);
```

The 'hashIndex' should be 'Index' rather than 'int'.

```
@@ -2039,8 +2039,7 @@ SearchCatCacheList(CatCache *cache,
#ifndef CATCACHE_FORCE_RELEASE
ct->dead &&
#endif
- ct->refcount == 0 &&
- (ct->c_list == NULL || ct->c_list->refcount == 0))
+ ct->refcount == 0)
CatCacheRemoveCTup(cache, ct);
}
```

Remove the dead code because we have a 'Assert(ct->c_list == NULL);'.

--
Regards,
ChangAo Chen