Merge #2917

2917: Remove old ci configurations r=hsbt a=hsbt

# Description:

Fixup #2915

______________

# Tasks:

- [ ] Describe the problem / feature
- [ ] Write tests
- [ ] Write code to solve the problem
- [ ] Get code review from coworkers / friends

I will abide by the [code of conduct](https://github.com/rubygems/rubygems/blob/master/CODE_OF_CONDUCT.md).


Co-authored-by: Hiroshi SHIBATA <hsbt@ruby-lang.org>

.travis.yml

@@ -11,38 +11,12 @@ env:
   - "TEST_TOOL=rubygems"
   - "TEST_TOOL=bundler RGV=master"
 rvm:
-  - 2.3.8
-  - 2.4.7
-  - 2.5.6
   - 2.6.4
 jobs:
   include:
-    - stage: linting
-      rvm: 2.6.4
-      env: "TEST_TOOL=rubygems"
-      script: util/ci.sh rubocop
-    - stage: test
-      rvm: 2.6.4
+    - rvm: 2.6.4
       env: "TEST_TOOL=bundler RGV=.. BDV=master"
-    - stage: test
-      rvm: jruby-9.2.8.0
-      env: "TEST_TOOL=rubygems"
-    - stage: test
-      rvm: ruby-head
-      env: "TEST_TOOL=rubygems"
-    - stage: test
-      rvm: ruby-head
-      env: "TEST_TOOL=bundler RGV=.. BDV=master"
-stages:
-  - linting
-  - test
 before_script:
   - util/ci.sh before_script
 script:
   - util/ci.sh script
-matrix:
-  allow_failures:
-    - rvm: ruby-head
-      env: "TEST_TOOL=rubygems"
-    - rvm: ruby-head
-      env: "TEST_TOOL=bundler RGV=.. BDV=master"

Manifest.txt

@@ -11,7 +11,6 @@ POLICIES.md
 README.md
 Rakefile
 UPGRADING.md
-appveyor.yml
 bin/gem
 bin/update_rubygems
 bundler/CHANGELOG.md