We don't track them accurately when in onchaind, but we don't want to:
onchaind can be restarted at any time.
Once it's all settled, we're clear to clean them up.
Before this, valgrind could complain about deferncing hout->key.peer:
Valgrind error file: valgrind-errors.10876
==10876== Invalid read of size 4
==10876== at 0x41F8AF: peer_on_chain (peer_control.h:127)
==10876== by 0x42340D: notify_new_block (peer_htlcs.c:1461)
==10876== by 0x40A08D: connect_block (chaintopology.c:96)
==10876== by 0x40A96B: topology_changed (chaintopology.c:313)
==10876== by 0x40AC85: add_block (chaintopology.c:384)
==10876== by 0x40ABF0: gather_previous_blocks (chaintopology.c:363)
==10876== by 0x4051B3: process_rawblock (bitcoind.c:410)
==10876== by 0x4044DD: bcli_finished (bitcoind.c:155)
==10876== by 0x454665: destroy_conn (poll.c:183)
==10876== by 0x454685: destroy_conn_close_fd (poll.c:189)
==10876== by 0x45DF89: notify (tal.c:240)
==10876== by 0x45E43A: del_tree (tal.c:400)
==10876== Address 0x6929208 is 2,120 bytes inside a block of size 2,416 free'd
==10876== at 0x4C2EDEB: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10876== by 0x45E513: del_tree (tal.c:421)
==10876== by 0x45E849: tal_free (tal.c:509)
==10876== by 0x41A8E9: handle_irrevocably_resolved (peer_control.c:1172)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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