remove gitlab task

.gitpod.yml

 image:
   file: .gitpod.Dockerfile
 
-gitlab:
-  prebuilds:
-    # enable for the default branch (defaults to true)
-    master: true
-
 tasks:
   - init: sdk use java 16.0.1.hs-adpt
-    prebuild: echo "Prebuild!"
+    prebuild: cd todolist; mvn compile
     command: cd todolist
 
 ports: