Unused field in InternalParquetRecordWriter Class

### Describe the enhancement requested

I have noticed that in the `org.apache.parquet.hadoop.InternalParquetRecordWriter` class, there is a field named `private final long rowGroupSize` that is initialized but never used within the class.

### Component(s)

Core, Protobuf

首先打开 org.apache.parquet.hadoop.InternalParquetRecordWriter 类，检查 rowGroupSize 字段及其引用。完成的标准是移除未使用的字段且不影响该类；运行相关的 Core 和 Protobuf 测试以确认更改。

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