SUP-19921: Fix the scheduled wastebin purge of a referenced page

[plyhun]

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[plyhun]

Note from TransactionManager::getLanguageId()

				// TODO: actually, we should always and only use the
				// session's languageId. Calling
				// ContentNodeHelper.getLanguageId() is done for backwards
				// compatibility, so that we don't change any current
				// behaviour. This will actually throw expected exceptions because
				// ContentNodeHelper.getLanguageId() isn't used by
				// ContentNodeResource. To fix this, one should remove the
				// get/setLanguageId() from ContentNodeHelper at some point.
				// Another point: this transaction may actually be for user=0
				// and sessionId=null (that happens when viewing a page
				// it seems). In that case, ContentNodeHelper.getLanguageId()
				// may still have a valid languageId - it should be checked whether
				// that is so, because then, one _has_ to use
				// ContentNodeHelper.getLanguageId() since the languageId can't
				// be retrieved if the sessionId is null.

Some of the current usages of ContentNodeHelper.getLanguageId() belongs to the wraps of UserLanguageFactory.getById()`, which looks like working the no-session case correclty. Other usages are somewhat unclear, whether expecting an exception on this method, so I hesitate so far removing it completely, as per comment above.