Remove ziplist dead code in object.c (#10751)

Remove some dead code in object.c, ziplist is no longer used in 7.0

Some backgrounds:
zipmap - hash: replaced by ziplist in #285
ziplist - hash: replaced by listpack in #8887
ziplist - zset: replaced by listpack in #9366
ziplist - list: replaced by quicklist (listpack) in #2143 / #9740

Moved the location of ziplist.h in the server.c