ticdc still block gc after all changefeeds are removed

[sdojjy]

if there is no changefeed, ticdc should remove the gc service from PD

reproduce steps:

1. add a changefeed
2. check the gc service checkpoint

 curl http://127.0.0.1:2379/pd/api/v1/gc/safepoint
{
  "service_gc_safe_points": [
    {
      "service_id": "gc_worker",
      "expired_at": 9223372036854775807,
      "safe_point": 443738300532916224
    },
    {
      "service_id": "ticdc-default-15674009460217235928",
      "expired_at": 1692814223,
      "safe_point": 443738442313498625
    }
  ],
  "gc_safe_point": 443738127517876224
}

4. remove the changefeed
5. check the gc service checkpoint again

curl http://127.0.0.1:2379/pd/api/v1/gc/safepoint
{
  "service_gc_safe_points": [
    {
      "service_id": "gc_worker",
      "expired_at": 9223372036854775807,
      "safe_point": 443739841939636224
    },
    {
      "service_id": "ticdc-default-15674009460217235928",
      "expired_at": 1692814223,
      "safe_point": 443738442313498625
    }
  ],
  "gc_safe_point": 443738442313498625
}