There's an important textual point to consider here, which might help resolve what seems like a contradiction from Cicero. Both of these texts, 'On Laws' and 'On Divination', are philosophical works in dialogue form. This was a common way of structuring such work, because it allowed multiple, sometimes conflicting perspectives to be presented in a clear and accessible way, achieving Cicero's aim of presenting complicated Greek philosophical ideas to his Latin readers. In Cicero's dialogues, each character is given a particular position to defend, and they usually argue against each other. Cicero often used himself as a character in these dialogues, but that doesn't necessarily mean that the things said by 'Cicero' were actually beliefs held by the real man, and there was no intention for consistency across the different dialogues. Indeed, the whole point was to present conflicts and allow the reader to decide which is most convincing. Tellingly, Cicero very rarely gives conclusions to these dialogues - he never passes a final judgement but leaves it to his audience.

Looking at these specific quotes, it's essential to consider what's going on in the whole text. Take the quote from de div, for example. As you say, it comes from the second book of the dialogue. In the first book, Cicero has his brother Quintus give a full philosophical defence of the various forms of divination, following the traditions of Roman religion and also the stoic school. In book 2 however, the character of 'Cicero' demolishes these arguments, asserting instead that divination is illogical and all those who claim to be able to tell the future are hucksters and charlatans. That's where your quote about haruspices fits in, and it makes total sense when the context is considered.

As for the de leg, again we need to think about the work as a whole. Here we have Cicero (or 'Cicero') imagining an ideal state, essentially Rome at some time in its past where all the social classes lived and worked in harmony for the common good. In Book 2 he is discussing the origins of law as coming from Nature, not Man, which meads on to discussions of religious laws. As Rome had always placed importance of omens and signs from the gods, it makes sense that he would praise augurs as a group of priests traditionally charged with maintaining good relations between the gods and humanity.

Which of these opinions on divination were actually held by the real Cicero is very difficult to tell, but I think it's more likely to be closer to the latter. Cicero was an augur himself, which is one of the reasons he was interested in the topic in the first place. Despite his philosophical scepticism, he remained a staunch traditionalist throughout his life, and so no doubt considered the rituals of seeking signs from the gods an essential foundation of the Roman state.