Remove the workaround to access HBase convertScanToString in hbase inputformat code

In the review for #707, we agree we should clean up the workaround to access HBase convertScanToString in hbase inputformat code.
```
// This is a workaround, to be removed when convertScanToString becomes public in hbase package.
Method converter;
try {
converter = TableMapReduceUtil.class.getDeclaredMethod("convertScanToString", Scan.class);
converter.setAccessible(true);
config.set(TableInputFormat.SCAN, (String) converter.invoke(null, scanner));
} catch (Exception e) {
throw new RuntimeException(e);
}
```

Search the Java HBase input-format code for the shown reflective access to TableMapReduceUtil.convertScanToString, then inspect the HBase API entry point it is intended to replace. Done means the workaround is removed while scan conversion behavior remains unchanged. The payload names no specific file or test, so identify the relevant HBase input-format tests before changing it.

Written by the indexing model from the issue text.