chore: remove dependabot PR assignees as team is not supported (#8824)

Author: edmundhung

.github/dependabot.yml

@@ -15,8 +15,6 @@ updates:
     # makes it so that also the PR title gets such prefix
     commit-message:
       prefix: "[C3] "
-    assignees:
-      - "@cloudflare/c3"
     reviewers:
       - "@cloudflare/c3"
     labels:
@@ -38,8 +36,6 @@ updates:
       interval: "daily"
       time: "06:00" # the workerd release starts at 00:30 UTC each day
     versioning-strategy: increase
-    assignees:
-      - "@cloudflare/wrangler"
     reviewers:
       - "@cloudflare/wrangler"
     labels: