Fix mutation

Author: manitgupta

v2/spanner-to-sourcedb/src/test/java/com/google/cloud/teleport/v2/templates/SpannerToSourceDbCustomShardIT.java

@@ -200,8 +200,6 @@ private void writeSpannerDataForSingers(int singerId, String firstName, String s
             .to(singerId)
             .set("FirstName")
             .to(firstName)
-            .set("migration_shard_id")
-            .to(shardId)
             .build();
     spannerResourceManager.write(m);
   }