Remove Slack notification.

See spring-projects#3519

Author: mp911de

Jenkinsfile

@@ -221,10 +221,6 @@ pipeline {
 post {
 changed {
 script {
-slackSend(
-color: (currentBuild.currentResult == 'SUCCESS') ? 'good' : 'danger',
-channel: '#spring-data-dev',
-message: "${currentBuild.fullDisplayName} - `${currentBuild.currentResult}`\n${env.BUILD_URL}")
 emailext(
 subject: "[${currentBuild.fullDisplayName}] ${currentBuild.currentResult}",
 mimeType: 'text/html',