test: Remove confusing assert_debug_log in wallet_reindex.py #34857

The wallet_reindex.py test has many issues:

• It uses a assert_debug_log to ensure the reindex happened via initload thread exit. However, no other test uses this pattern, because restart_node already achieves the same internally (via getmempoolinfo.loaded).
• The assert_debug_log may intermittently fail, because the initload thread exit log may happen at any time after the inner thread function (lambda) is fully done.
• The test uses an node.syncwithvalidationinterfacequeue() without any explanation. No other test uses this pattern, because all wallet RPCs, in particular the next one (gettransaction) call it internally (via BlockUntilSyncedToCurrentChain).

Fix all issues by removing all confusing, useless, and brittle calls.

Example failure: https://github.com/bitcoin/bitcoin/actions/runs/22671604602/job/65716917459?pr=34419#step:11:22339

...
 node0 2026-03-04T13:55:23.784715Z (mocktime: 2026-03-04T22:15:17Z) [scheduler] [validationinterface.cpp:185] [operator()] [validation] UpdatedBlockTip: new block hash=24b5cc4c1352bc8841ecbe67a43827acd1adc609bd26b2691e80e89b97eff135 fork block hash=24a4dc8be9c157ac31913397d8bb1653900e12b55539c234039559fdeb6dd2fb (in IBD=true) 
 node0 2026-03-04T13:55:23.784851Z (mocktime: 2026-03-04T22:15:17Z) [initload] [util/thread.cpp:22] [TraceThread] initload thread exit 
 test  2026-03-04T13:55:23.813824Z TestFramework (ERROR): Unexpected exception: 
                                   Traceback (most recent call last):
                                     File "/home/admin/actions-runner/_work/_temp/test/functional/test_framework/test_framework.py", line 142, in main
                                       self.run_test()
                                     File "/home/admin/actions-runner/_work/_temp/build/test/functional/wallet_reindex.py", line 90, in run_test
                                       self.birthtime_test(node, miner_wallet)
                                     File "/home/admin/actions-runner/_work/_temp/build/test/functional/wallet_reindex.py", line 64, in birthtime_test
                                       with node.assert_debug_log(expected_msgs=["initload thread exit"]):
                                     File "/usr/lib/python3.12/contextlib.py", line 144, in __exit__
                                       next(self.gen)
                                     File "/home/admin/actions-runner/_work/_temp/test/functional/test_framework/test_node.py", line 607, in assert_debug_log
                                       self._raise_assertion_error(f'Expected message(s) {remaining_expected!s} '
                                     File "/home/admin/actions-runner/_work/_temp/test/functional/test_framework/test_node.py", line 241, in _raise_assertion_error
                                       raise AssertionError(self._node_msg(msg))
                                   AssertionError: [node 0] Expected message(s) ['initload thread exit'] not found in log:

Diff to reproduce failure:

diff --git a/src/util/thread.cpp b/src/util/thread.cpp
index 0fde73c4e2..de4c05e752 100644
--- a/src/util/thread.cpp
+++ b/src/util/thread.cpp
@@ -8,2 +8,3 @@
 #include <util/log.h>
+#include <util/time.h>
 #include <util/threadnames.h>
@@ -21,2 +22,3 @@ void util::TraceThread(std::string_view thread_name, std::function<void()> threa
         thread_func();
+    UninterruptibleSleep(999ms);
         LogInfo("%s thread exit", thread_name);
diff --git a/test/functional/wallet_reindex.py b/test/functional/wallet_reindex.py
index 71ab69e01b..649df4301a 100755
--- a/test/functional/wallet_reindex.py
+++ b/test/functional/wallet_reindex.py
@@ -62,2 +62,3 @@ class WalletReindexTest(BitcoinTestFramework):
 
+        import time; time.sleep(1) # Wait for previous initload thread to exit fully
         # Reindex and wait for it to finish

Before on master: Test fails After on this pull: Test passes

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #34879 (test, wallet: overhaul wallet_reindex test to wallet_birthtime by rkrux)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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cc @furszy As the author of the code you may be qualified to nack/ack this?

Concept ACK fa30951 for the overall improvement in the test.

ACK fa30951af5b174a1ee5e1c23d84b115c542a9570 if this PR needs to be backported.

These changes are smaller, to-the-point, and easier to review compared to the test revamp PR I have raised separately.

Backported to 31.x in #34800.