closed #4020: cocos_files.json should be auto-generated by CocosRobot.
issue #4020: Updates before-install.sh. and comment fix in generate-cocosfiles.sh.
issue #4020: Typo fix, elif -> if.
Merge pull request #5344 from dumganhar/iss4020-auto-cocos-files

closed #4020: cocos_files.json should be auto-generated by CocosRobot.