Remove obsolete CircleCI config

Builds have been stopped, we can remove the CircleCI config file.

Signed-off-by: SuperQ <superq@gmail.com>

.circleci/config.yml

@@ -1,33 +0,0 @@
----
-# Prometheus has switched to GitHub action.
-# Circle CI is not disabled repository-wise so that previous pull requests
-# continue working.
-# This file does not generate any CircleCI workflow.
-
-version: 2.1
-
-executors:
-  golang:
-    docker:
-      - image: busybox
-
-jobs:
-  noopjob:
-    executor: golang
-
-    steps:
-      - run:
-          command: "true"
-
-workflows:
-  version: 2
-  prometheus:
-    jobs:
-      - noopjob
-    triggers:
-      - schedule:
-          cron: "0 0 30 2 *"
-          filters:
-            branches:
-              only:
-                - main