Yes it's legal to take them down. Anything put up by ordinary citizens like that can be taken down as well. Only things put up by the city or with special permits are prohibited to remove or damage.

Who told you they had razor blades behind them? There's some odd pernicious myth, usually about fascist posters that they put razors behind them yet there's little evidence it was ever a widespread thing (among other things it turns something cities ignore into a potential crime).

I would suggest a knife to cut 2-3 pieces of tape then just tear them off to do so quickly. The thing to watch out for is there may be little loyal zionists watching who might try and take your picture and try and claim hate crimes or whatever, best not to be photographed anyways as they'll slander you. I once took down some Falun Gong posters and some lady appeared out of nowhere and tried to take my picture but she was too far away and I just turned and ran off before she could get closer lol.