fix(ci): Move snapshot bucket overwrite permission to vm (#256)

Author: usmanmani1122

.github/workflows/trigger-mainfork-snapshot.yaml

@@ -1,5 +1,4 @@
 env:
-  BUCKET_NAME: 'agoric-snapshots-public'
   PROJECT_ID: 60745596728
 
 jobs:
@@ -75,11 +74,6 @@ jobs:
               exit 1
             fi
 
-            gsutil rm \
-              -a \
-              -f \
-              "gs://${{ env.BUCKET_NAME }}/mainfork-snapshots/keyring-test.tar.gz" \
-              "gs://${{ env.BUCKET_NAME }}/mainfork-snapshots/priv_validator_state.json"
             IMAGE_TAG="$IMAGE_TAG" ./mainfork-snapshot.sh
           fi
         working-directory: scripts