No. Firstly, the U.K. hasn't left the UK - not yet anyway. Secondly, all European legislation that applies only applies because it has been made law locally in the UK. In order to change that, the U.K. Parliament would need to amend the existing leglislation or enact new. Even if it did that, it would take years to go through everything and many laws would not be changed at all. The view of certain civil servants (Gus O'lDonnell for instance) is that there are so many pieces of legislations that will need amending, the most legislations will remain as is, permanently.
My take on it is that it will be in force at least until the formal leaving of the EU (two years from invoking article 50). After that, if it is an act of parliament, then the wording of the act would need to be looked at to see if we could stop showing cookie consent to UK visitors.
Also I expect all laws that mention the EU will be looked at in light of Brexit by the new Brexit Ministry (otherwise known as the Ministry of Administrative Affairs).
I would disagree with the cookie law being a long way down the list of laws that require attention. If you calculate the lost productivity from people having to spend the time to dismiss cookie messages, repealing the law will make the UK workforce more competitive compared to that in the EU.
Oh, don't get me wrong, the cookie law was badly thought through and is a major annoyance for me and other having to click OK on every first time visit to a site. If you clear your cookies frequently you've got to click that agreement again. I'd love to see the back of it, but I doubt it will go, especially with the likelihood of websites serving EU audiences.
Guys please also bear in mind that when a European Directive is enacted, this is a requirement for European states to enact their own lawa, it is not a law in itself. When that happened in this case, the UK implemented much tougher rules than almost all other countries with the exception of the Netherlands. In the end, it's a British law. You may also have forgotten that when it came into force, the first website which was forced to make changes was actually a British Gov't department one. The ONLY way that this law would be changed - in my view - would be if there was pressure to do some from British businesses. I don't see that many British businesses caring about it - and with the trend towards stricter and stricter privacy, it's really not likely any time in the next decade.
That law was an example of how it can be badly implemented, and a European version might have been better, however, that's how the EU works. Each member state has to have it's own law. They can, of course, make it stricter to meet their own local requirements, as per the examples you cited.
I think we, as webmasters, and also as users, all know it could have been significantly improved to avoid the annoyance.