[gnome-control-center] Revert "ci: Build Docker images when Dockerfile changes"

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit c2c7547e78a588200ce4833f0500150bb7bf2639
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sun Nov 18 20:55:52 2018 -0200

    Revert "ci: Build Docker images when Dockerfile changes"
    
    This reverts commit 1d4d9953230d727b4d6448ac4422e9d8b518ea7f.

 .gitlab-ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 703338e1a..89254b9bd 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -317,8 +317,8 @@ ppc64le:
   services:
     - docker:dind
   only:
-    changes:
-      - '.gitlab-ci/Dockerfile'
+    variables:
+      - $CRON_TASK == "BUILD_CI_IMAGES"
 
   script:
     # Skip the build (if requested)