Cleanup code for max-file-group-size-bytes in Iceberg rewrite files.

### Feature Request / Improvement

max-file-group-size-bytes and MAX_FILE_GROUP_SIZE_BYTES_DEFAULT are present in two places thus can lead to confusion.
https://github.com/apache/iceberg/blob/main/api/src/main/java/org/apache/iceberg/actions/RewriteDataFiles.java#L76
https://github.com/apache/iceberg/blob/main/core/src/main/java/org/apache/iceberg/actions/SizeBasedFileRewritePlanner.java#L106

I suggest we keep the configs in RewriteDataFiles as the external facing interface.

### Query engine

None

### Willingness to contribute

- [x] I can contribute this improvement/feature independently
- [ ] I would be willing to contribute this improvement/feature with guidance from the Iceberg community
- [ ] I cannot contribute this improvement/feature at this time