Remove caching of ivy repo from pipeline

* following an internal discussion, we'd rather be sure to build
  everything from scratch in the runner, or version hell ensues

.gitlab-ci.yml

@@ -4,13 +4,6 @@
 # but an image with a JVM speeds up the build a bit.
 image: java:8
 
-cache:
-        paths:
-                - .ivy2/
-
-variables:
-        SBT_OPTS: "-Divy.home=.ivy2/ -Dsbt.ivy.home=.ivy2/ -Xss16M"
-
 before_script:
   # Enable the usage of sources over https
   - apt-get update -yqq