Revert "Add /rerun slash command for failed internal checks"

.github/commands/rerun.yml

@@ -1,14 +0,0 @@
----
-trigger: rerun
-title: Rerun failed internal checks
-surfaces:
-  - pull_request
-description: >
-  Finds all failed internal CI checks for this PR and reruns their failed jobs.
-
-steps:
-  - type: repository_dispatch
-    eventType: rerun-workflow
-  - type: fill
-    submit_form: true
-    template: "Rerun has been triggered."