[ci] Disable download tests unless specifically invoked

Tests can be enabled/disabled using the following in the commit message
* Run Download: `ci-run-dl`
* Skip Core: `ci-skip`
* Skip Quick & Core: `ci-skip-all`
(replace "-" by a space " ")

.github/workflows/core.yml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 jobs:
   tests:
     name: Core Tests
-    if: "!contains(github.event.head_commit.message, 'ci skip all')"
+    if: "!contains(github.event.head_commit.message, 'ci skip')"
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: true

.github/workflows/download.yml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 jobs:
   tests:
     name: Download Tests
-    if: "!contains(github.event.head_commit.message, 'ci skip dl') && !contains(github.event.head_commit.message, 'ci skip all')"
+    if: "contains(github.event.head_commit.message, 'ci run dl')"
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: true

.travis.yml.disabled

@@ -1,38 +0,0 @@
-language: python
-python:
-  - "2.6"
-  - "2.7"
-  - "3.2"
-  - "3.3"
-  - "3.4"
-  - "3.5"
-  - "3.6"
-  - "pypy"
-  - "pypy3"
-dist: trusty
-env:
-  - YTDL_TEST_SET=core
-jobs:
-  include:
-    - python: 3.7
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - python: 3.8
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - python: 3.8-dev
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - env: JYTHON=true; YTDL_TEST_SET=core
-    - name: flake8
-      python: 3.8
-      dist: xenial
-      install: pip install flake8
-      script: flake8 .
-  fast_finish: true
-  allow_failures:
-    - env: YTDL_TEST_SET=download
-    - env: JYTHON=true; YTDL_TEST_SET=core
-before_install:
-  - if [ "$JYTHON" == "true" ]; then ./devscripts/install_jython.sh; export PATH="$HOME/jython/bin:$PATH"; fi
-script: ./devscripts/run_tests.sh