tests: Add Python dead code linter (vulture)

.travis/lint_04_install.sh

@@ -8,3 +8,4 @@ export LC_ALL=C
 
 travis_retry pip install codespell==1.13.0
 travis_retry pip install flake8==3.5.0
+travis_retry pip install vulture==0.29

test/lint/lint-python-dead-code.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+#
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Find dead Python code.
+
+export LC_ALL=C
+
+if ! command -v vulture > /dev/null; then
+    echo "Skipping Python dead code linting since vulture is not installed. Install by running \"pip3 install vulture\""
+    exit 0
+fi
+
+vulture \
+    --min-confidence 60 \
+    --ignore-names "argtypes,connection_lost,connection_made,converter,data_received,daemon,errcheck,get_ecdh_key,get_privkey,is_compressed,is_fullyvalid,msg_generic,on_*,optionxform,restype,set_privkey" \
+    $(git ls-files -- "*.py" ":(exclude)contrib/")