ci: remove Unity 2021.1 version from tests (#1764)

Author: ashwinimurt

.yamato/project.metafile

@@ -41,7 +41,6 @@ projects:
       - name: com.unity.netcode.adapter.utp
         path: com.unity.netcode.adapter.utp
     test_editors:
-      - 2021.1
       - 2021.2
       - 2020.3
       - trunk