fix(ci): remove placeholder entry blocking Dependabot

This dependabot.yml carries GitHub's unedited placeholder alongside a real,
correct entry:

    - package-ecosystem: ""   # See documentation for possible values

An empty package-ecosystem fails schema validation and GitHub rejects the WHOLE
file, so the real github-actions entry has never run either.

MEASURED: the three estate repos in exactly this state (blocky-writer, jtv-lang,
lcb-website) have 0 Dependabot PRs between them, while comparable repos with
valid configs have 7-63 (aerie 7, standards 8, affinescript 16, hypatia 63).
All three do have .github/workflows/ to update.

Removing the stub leaves the real entry intact and unblocks it. Any entry that
lacked a groups: block gets one, so an ecosystem bump arrives as ONE PR rather
than one per dependency.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

.github/dependabot.yml

@@ -5,10 +5,6 @@
 
 version: 2
 updates:
-  - package-ecosystem: "" # See documentation for possible values
-    directory: "/" # Location of package manifests
-    schedule:
-      interval: "daily"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: