Fix reindex yaml test

Reindex task may not have completed by time status
is called, so remove assertion that relies on this.
Following assertions are set in the action which
starts task, so will be correct whether or not task
has completed.

Author: parkertimmins

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/migrate/20_reindex_status.yml

@@ -60,7 +60,6 @@ setup:
   - do:
       indices.get_migrate_reindex_status:
         index: "my-data-stream"
-  - match: { complete: true }
   - match: { total_indices_in_data_stream: 1 }
   - match: { total_indices_requiring_upgrade: 0 }
   - match: { successes: 0 }