universities don't really care all that much if you do law or don't do maths, and they don't really care if you have ten thousand a levels.
picking up an extra as might damage your chances of getting really top grades in your a2s, and any combination of your as levels, be it four or three, would be fine to apply to uni with. if it were me, i'd drop law only because it isn't as respected, you're right, not because universities will not give you an offer because you have it.
your university ambitions will change between now and july, when imo you should begin to finalise your course/draw up a final list of your courses. for example, this time last year i wanted to do politics and german. i'm going to do hebrew studies now, haha, and might do english and russian with arabic for a second degree. times change, my lad. it is good you're thinking about it now but stick to working hard on your as's.