Use the default dependabot labeling (thanos-io#7457)

Dependabot already includes `dependencies` on PRs. Removing the config
will cause it to also include an ecosystem label like `go`.

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

.github/dependabot.yml

@@ -5,15 +5,12 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
-    labels: ["dependencies"]
     open-pull-requests-limit: 20
   - package-ecosystem: "docker"
     directory: "/"
     schedule:
       interval: "weekly"
-    labels: ["dependencies"]
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: 
       interval: weekly
-    labels: ["dependencies"]