Clean up redundant access modifiers from oozie interfaces

public interface RestConstants {
    public static final String VERSIONS = "versions";
    public static final String JOB = "job";
...
}

public interface JsonTags {
    public static final String OOZIE_SAFE_MODE = "safeMode"; //Applicable for V0 only
    public static final String OOZIE_SYSTEM_MODE = "systemMode";
...
}