There is some room for cleanup in the jdk/nio/zipfs tests. In detail:
- Fix warnings in test/jdk/jdk/nio/zipfs/Demo.java (no real testcase but Demo coding)
- change some calls of Runtime.version().major() to Runtime.version().feature() (the former is deprecated)
- change occurences of new Integer() to Integer.valueOf()
- change occurences of class.newInstance() to class.getDeclaredConstructor().newInstance()
- remove unused variables
- move test/jdk/jdk/nio/zipfs/jarfs/JFSTester.java to test/jdk/jdk/nio/zipfs/JFSTester.java (not using the jarfs subfolder). There is no need for this specific subfolder, given that MultiReleaseJarTest.java neither isn't in the jarfs subfolder