delete useless comment

Author: kkewwei

server/src/main/java/org/opensearch/index/mapper/FlatObjectFieldMapper.java

@@ -133,7 +133,6 @@ public static class Builder extends FieldMapper.Builder<Builder> {
         private int depthLimit = Integer.MAX_VALUE;
         private final IndexAnalyzers indexAnalyzers;
 
-        // Visible for testing
         public Builder(String name, IndexAnalyzers indexAnalyzers) {
             super(name, Defaults.FIELD_TYPE);
             builder = this;