Remove dummy circleci config

The 20.10 branch reached EOL, so we can probably remove this
one again.

This reverts commit a3d53e319f.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.circleci/config.yml

@@ -1,19 +0,0 @@
-# This is a dummy CircleCI config file to avoid GitHub status failures reported
-# on branches that don't use CircleCI. This file should be deleted when all
-# branches are no longer dependent on CircleCI.
-version: 2
-
-jobs:
-  dummy:
-    docker:
-      - image: busybox
-    steps:
-      - run:
-          name: "dummy"
-          command: echo "dummy job"
-
-workflows:
-  version: 2
-  ci:
-    jobs:
-      - dummy