Clean up: remove two unused features, assume four more

[rustyrussell]

Removed:

• initial_routing_sync (only had an effect if gossip_queries not supported)
• option_anchor_outputs (only supported by older experimental-only CLN builds)

I looked at all node_announcements on my node. There are 449 nodes apparently running a 4-year-old LND version (features hex 2200), which have 3+ year old channels. @Roasbeef points out that they already will have their channel_updates ignored due to lack of htlc_maximum_msat which is now required by LND and CLN, at least).

Features you can now assume (you should probably still set it for now, but you can stop checking it).

• var_onion_optin (all but 6 nodes)
• option_data_loss_protect (all but 11 nodes)
• option_static_remotekey (all but 16 nodes)

gossip_queries is now slightly repurposed: if you don't offer this, it means you won't give useful gossip (so you should not query such nodes, nor consider them when trying to figure out if you've got all the gossip).