test-trees: remove maaku tree.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
incremental-proof-tree: embed an incremental proof in each block.

This is a different approach from the previous "include all the blocks"
approach: we only store blocks on the previous block's path-to-genesis,
plus the previous block.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>