Remove unused parameters and obsolete code fragments

This affects:
* Some null checks before instanceof checks
* CouchDBDao.collectUnansweredQuestionIds()
* DeprecatedApiInterceptorHandler.getDeprecatedApiAnnotation()
* CacheControlInterceptorHandler.getCacheControlAnnotation()
* CacheControlInterceptorHandler.setCacheControlResponseHeader()
* FeedbackService - userService private field