Drop Jenkinsfile

We run in gitlab-ci now

Jenkinsfile

-pipeline {
-    agent { docker 'godiug/librem5ci:latest' }
-    stages {
-        stage('Build') {
-            steps {
-                checkout scm
-                sh 'rm -rf _build'
-                sh 'meson . _build'
-                sh 'ninja -C _build'
-            }
-        }
-        stage('Test') {
-            steps {
-                sh 'xvfb-run ninja -C _build test'
-            }
-        }
-    }
-}