Upgrade bitcoind to 0.18.0~dfsg-1+
Originally created by @intrigeri on #16826 (Redmine)
IIRC, the maintenance plan for bitcoind was to build custom backports of the sid package. We currently run 0.17.1~dfsg-1~tails1 while 0.18.0~dfsg-1 is in sid since a month and a half.