In tiered storage, the block manager (WT_BM) holds a set of block handles (WT_BLOCK), each represents a single object in the Btree. These block handles are created on demand as objects are referenced, but they are never cleaned up. Since these can grow without bound (as more flush_tier calls create new objects), we'll need to "expire" them. Removing them from WT_BM->handle_array will reduce the ref count in the connection's list of block handles (in WT_CONNECTION_IMPL->block_hash) and should remove it from the connection list when the last ref is removed.