Merge #16961: test: Remove python dead code linter

f4beb49 test: Remove python dead code linter (Wladimir J. van der Laan)

Pull request description:

  Primarily I'd like to remove this because it is very imprecise, due to Python's dynamic nature, giving it a large list of false positives that need to be listed as exceptions. See for example #16906.

  It's also a frequent source of complaints. I'm doubtful of the usefulness of checking for dead code in a linter in the first place.
  Having some dead code in the test framework for a while is not a
  disaster.

ACKs for top commit:
  sdaftuar:
    utACK f4beb49
  practicalswift:
    ACK f4beb49 -- diff looks correct
  jamesob:
    ACK bitcoin/bitcoin@f4beb49

Tree-SHA512: 329b1555210311d5d15799fd2cb794b3208b0ac4d8a2ffaf4dece1bcc3e0e8b1fe952d5e7a394f94a98919cab579fb579eae7db2a796cc9a1a42ef495dd17507

Author: MarcoFalke

ci/lint/04_install.sh

@@ -8,7 +8,6 @@ export LC_ALL=C
 
 travis_retry pip3 install codespell==1.15.0
 travis_retry pip3 install flake8==3.7.8
-travis_retry pip3 install vulture==1.0
 
 SHELLCHECK_VERSION=v0.6.0
 curl -s "https://storage.googleapis.com/shellcheck/shellcheck-${SHELLCHECK_VERSION}.linux.x86_64.tar.xz" | tar --xz -xf - --directory /tmp/