Remove non available stack release versions from integration CI tests

Author: alexcams

.travis.yml

@@ -10,8 +10,6 @@ jobs:
       env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=7.current
     - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.previous
     - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.current
-    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.next
-    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.future
     - stage: "Secure Integration Tests"
       env: SECURE_INTEGRATION=true INTEGRATION=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.current SNAPSHOT=true
     - env: SECURE_INTEGRATION=true INTEGRATION=true LOG_LEVEL=info ELASTIC_STACK_VERSION=7.current