buf_pool_t: Remove n_frames, max_size, and blocks_of_frames.
The current buffer pool size is in curr_size.

buf_pool_init(): Remove parameter max_size.

buf_pool_get_max_size(), buf_pool_is_block(): Remove.

buf_block_align(): Do not assume that the buffer pool is allocated
in one chunk.  Replace dependency on buf_pool->blocks_of_frames
with a call to buf_page_hash_get().