Merge #16898: test: Remove connect_nodes_bi

fadfd844de test: Remove unused connect_nodes_bi (MarcoFalke)
fa3b9ee8b2 scripted-diff: test: Replace connect_nodes_bi with connect_nodes (MarcoFalke)
faaee1e39a test: Use connect_nodes when connecting nodes in the test_framework (MarcoFalke)
1111bb91f5 test: Reformat python imports to aid scripted diff (MarcoFalke)

Pull request description:

  By default all test nodes are connected in a chain. However, instead of just a single connection between each pair of nodes, we end up with up to four connections for a "middle" node (two outbound, two inbound, from each side).

  This is generally redundant (tx and block relay should succeed with just a single connection) and confusing. For example, test timeouts after a call to `sync_` may be racy and hard to reproduce. On top of that, the test `debug.log`s are hard to read because txs and block invs may be relayed on the same connection multiple times.

  Fix this by inlining `connect_nodes_bi` in the two tests that need it, and then replace it with a single `connect_nodes` in all other tests.

  Historic background:

  `connect_nodes_bi` has been introduced as a (temporary?) workaround for bug #5113 and #5138, which has long been fixed in #5157 and #5662.

ACKs for top commit:
  laanwj:
    ACK fadfd844de
  jonasschnelli:
    utACK fadfd844de - more of less a cleanup PR.
  promag:
    Tested ACK fadfd844de, ran extended tests.

Tree-SHA512: 2d027a8fd150749c071b64438a0a78ec922178628a7dbb89fd1212b0fa34febd451798c940101155d3617c0426c2c4865174147709894f1f1bb6cfa336aa7e24

test/functional/rpc_rawtransaction.py

@@ -17,7 +17,13 @@ from decimal import Decimal
 from io import BytesIO
 from test_framework.messages import CTransaction, ToHex
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal, assert_raises_rpc_error, connect_nodes_bi, hex_str_to_bytes
+from test_framework.util import (
+    assert_equal,
+    assert_raises_rpc_error,
+    connect_nodes,
+    hex_str_to_bytes,
+)
+
 
 class multidict(dict):
     """Dictionary that allows duplicate keys.
@@ -53,7 +59,7 @@ class RawTransactionsTest(BitcoinTestFramework):
 
     def setup_network(self):
         super().setup_network()
-        connect_nodes_bi(self.nodes, 0, 2)
+        connect_nodes(self.nodes[0], 2)
 
     def run_test(self):
         self.log.info('prepare some coins for multiple *rawtransaction commands')