Merge bitcoin#20691: ci, doc: Travis CI features and mentions cleanup

95487b0 doc: Drop mentions of Travis CI as it is no longer used (Hennadii Stepanov)
09d105e ci: Drop travis_fold feature as Travis CI is no longer used (Hennadii Stepanov)

Pull request description:

  As Travis CI is no longer used, this PR:
  - drops `travis_fold` feature
  - drops mentions of Travis CI in docs

ACKs for top commit:
  MarcoFalke:
    ACK 95487b0

Tree-SHA512: 2e259bb8b1e37bcefc1251737bb2716f06ddb57c490010b373825c4e70f42ca38efae69a2f63f21f577d7cee3725b94097bdddbd313f8ebf499281cf97c53cef

.cirrus.yml

@@ -58,8 +58,6 @@ task:
   << : *CREDITS_TEMPLATE
   setup_script:
     - set -o errexit; source ./ci/test/00_setup_env.sh
-  before_install_script:
-    - set -o errexit; source ./ci/test/03_before_install.sh
   install_script:
     - set -o errexit; source ./ci/lint/04_install.sh
   before_script:

README.md

@@ -62,7 +62,8 @@ There are also [regression and integration tests](/test), written
 in Python.
 These tests can be run (if the [test dependencies](/test) are installed) with: `test/functional/test_runner.py`
 
-The Travis CI system makes sure that every pull request is built for Windows, Linux, and macOS, and that unit/sanity tests are run automatically.
+The CI (Continuous Integration) systems make sure that every pull request is built for Windows, Linux, and macOS,
+and that unit/sanity tests are run automatically.
 
 ### Manual Quality Assurance (QA) Testing
 

ci/test/05_before_script.sh

@@ -36,7 +36,5 @@ if [ -z "$NO_DEPENDS" ]; then
   DOCKER_EXEC $SHELL_OPTS make $MAKEJOBS -C depends HOST=$HOST $DEP_OPTS
 fi
 if [ -n "$PREVIOUS_RELEASES_TO_DOWNLOAD" ]; then
-  BEGIN_FOLD previous-versions
   DOCKER_EXEC test/get_previous_releases.py -b -t "$PREVIOUS_RELEASES_DIR" "${PREVIOUS_RELEASES_TO_DOWNLOAD}"
-  END_FOLD
 fi

ci/test_run_all.sh

@@ -7,6 +7,5 @@
 export LC_ALL=C.UTF-8
 
 set -o errexit; source ./ci/test/00_setup_env.sh
-set -o errexit; source ./ci/test/03_before_install.sh
 set -o errexit; source ./ci/test/04_install.sh
 set -o errexit; source ./ci/test/05_before_script.sh

doc/developer-notes.md

@@ -621,7 +621,7 @@ General Dash Core
   - *Rationale*: RPC allows for better automatic testing. The test suite for
     the GUI is very limited.
 
-- Make sure pull requests pass Travis CI before merging.
+- Make sure pull requests pass CI before merging.
 
   - *Rationale*: Makes sure that they pass thorough testing, and that the tester will keep passing
      on the master branch. Otherwise, all new pull requests will start failing the tests, resulting in
@@ -1068,7 +1068,7 @@ Scripted diffs
 --------------
 
 For reformatting and refactoring commits where the changes can be easily automated using a bash script, we use
-scripted-diff commits. The bash script is included in the commit message and our Travis CI job checks that
+scripted-diff commits. The bash script is included in the commit message and our CI job checks that
 the result of the script is identical to the commit. This aids reviewers since they can verify that the script
 does exactly what it is supposed to do. It is also helpful for rebasing (since the same script can just be re-run
 on the new master commit).

test/functional/README.md

@@ -23,7 +23,7 @@ don't have test cases for.
 - The oldest supported Python version is specified in [doc/dependencies.md](/doc/dependencies.md).
   Consider using [pyenv](https://github.com/pyenv/pyenv), which checks [.python-version](/.python-version),
   to prevent accidentally introducing modern syntax from an unsupported Python version.
-  The Travis linter also checks this, but [possibly not in all cases](https://github.com/bitcoin/bitcoin/pull/14884#discussion_r239585126).
+  The CI linter job also checks this, but [possibly not in all cases](https://github.com/bitcoin/bitcoin/pull/14884#discussion_r239585126).
 - See [the python lint script](/test/lint/lint-python.sh) that checks for violations that
   could lead to bugs and issues in the test code.
 - Use [type hints](https://docs.python.org/3/library/typing.html) in your code to improve code readability