Delete OS dependent check in JdkFinder.getExecutable()

The check below is too OS dependent and should be deleted.
...
        binPath += File.separatorChar + "bin" + File.separatorChar + executable;
        File toolFile = new File(binPath);
==> if (!toolFile.exists()) {
            throw new RuntimeException(binPath + " does not exist");
        }
...

On windows if executable is specified as e.g. 'java', without '.exe', the File exists() will fail. But it's still possible to run executable.