Remove dependabot again

For a project of this size, and with this release frequency, dependabot
causes too much noise and creates too many useless pull requests. It is
more efficient for me to update all dependency versions prior to a
release.

.github/dependabot.yml

@@ -1,12 +0,0 @@
-version: 2
-updates:
-  - package-ecosystem: "maven"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-    ignore:
-      - dependency-name: "org.slf4j:*"
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "weekly"