Remove Windows and macOS CI for now

For some reason our Windows and macOS runners don't work for this
project right now. The OS difference probably isn't relevant here
anyway.

.gitlab-ci.yml

@@ -25,20 +25,6 @@ tests:jdk-17:
   extends: .tests
   image: openjdk:17-jdk-slim
 
-tests:macos:
-  extends: .tests
-  before_script:
-    - export GRADLE_USER_HOME=`pwd`/.gradle
-  tags:
-    - macos
-
-tests:windows64:
-  extends: .tests
-  before_script: []
-  script: gradlew.bat %GRADLE_ARGS% check
-  tags:
-    - windows
-
 publish:
   stage: deploy
   before_script: