ci: Remove ineffective pip ecosystem from Dependabot

The pip ecosystem doesn't scan .pre-commit-config.yaml files.
Pre-commit hook updates will be handled by pre-commit.ci instead.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: tablackburn

.github/dependabot.yml

@@ -9,13 +9,3 @@ updates:
     labels:
       - "dependencies"
       - "github-actions"
-
-  - package-ecosystem: "pip"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-    commit-message:
-      prefix: "ci"
-    labels:
-      - "dependencies"
-      - "pre-commit"