ci: Remove unmaintained extended_lint

Author: MarcoFalke

.travis.yml

@@ -43,7 +43,6 @@ before_cache:
 stages:
   - lint
   - test
-  - extended-lint
 env:
   global:
     - CI_RETRY_EXE="travis_retry"
@@ -82,19 +81,6 @@ jobs:
       script:
         - set -o errexit; source ./ci/lint/06_script.sh
 
-    - stage: extended-lint
-      name: 'extended lint [runtime >= 60 seconds]'
-      env:
-      cache: false
-      language: python
-      python: '3.5'
-      install:
-        - set -o errexit; source ./ci/extended_lint/04_install.sh
-      before_script:
-        - set -o errexit; source ./ci/lint/05_before_script.sh
-      script:
-        - set -o errexit; source ./ci/extended_lint/06_script.sh
-
     - stage: test
       name: 'ARM  [GOAL: install]  [unit tests, functional tests]'
       arch: arm64