Remove -txindex=1 from seednode's bitcoin.conf

This change needs thorough review before being merged.

See bitcoin-core Issue "Remove txindex migration code #22626":
  bitcoin/bitcoin#22626
And comment about change not having a release note:
  bitcoin/bitcoin#22626 (comment)

See src:   https://github.com/bitcoin/bitcoin/blob/v23.0/src/txdb.cpp#L35

For API test suites:
  This change is backward compatible for bitcoin-core v22.
  This change has not been tested against bitcoin-core v21, v20, v19.

Change needs to be thoroughly tested with desktop UI.

seednode/bitcoin.conf

@@ -2,7 +2,6 @@ server=1
 daemon=1
 listen=1
 discover=1
-txindex=1
 dbcache=1337
 maxconnections=1337
 peerbloomfilters=1