The buf_pool->zip_clean list is only needed for debugging, or for
recomputing buf_pool->page_hash when resizing the buffer pool. Buffer
pool resizing was never fully implemented. Remove the resizing code,
and define buf_pool->zip_clean only in debug builds.

buf_pool->zip_clean, buf_LRU_insert_zip_clean(): Enclose in
#if defined UNIV_DEBUG || UNIV_BUF_DEBUG.

buf_chunk_free(), buf_chunk_all_free(), buf_pool_shrink(),
buf_pool_page_hash_rebuild(), buf_pool_resize(): Remove (unreachable code).

rb:671 approved by Inaam Rana