btr_compress(): Pass the correct page_zip to btr_node_ptr_set_child_page_no().

page_mem_free(): Remove parameter mtr.  Do not call page_zip_clear_rec() here.

page_cur_delete_rec(): Call page_zip_clear_rec() here.  Decrement PAGE_N_RECS
only after calling page_mem_free().  Assert page_zip_validate().