This change removes the "zipped index files" feature, which was introduced as part of JDK-8141492: Implement search feature in javadoc.
In a nutshell, the feature is being removed for the following reasons.
1. It doesn't work correctly
2. It targets only index files, though there are plenty of HTML pages having a similar size
3. HTTP compression is widespread and provides a more uniform and robust solution
See the below Comments section and the linked RFR thread for more details.