btr_search_sys::parts[]: A single structure for the partitions of
the adaptive hash index. Replaces the 3 separate arrays:
btr_search_latches[], btr_search_sys->hash_tables,
btr_search_sys->hash_tables[i]->heap.

hash_table_t::heap, hash_table_t::adaptive: Remove.

ha0ha.cc: Remove. Move all code to btr0sea.cc.