By Emma Wilson Britney Spears has quit Instagram again in a move that has coincided with the 20th anniversary of her iconic hit Toxic. The 42-year-old has deleted her account on the social media site just days after she announced she was never making music again, and had quit the industry for good. Britney’s 43 million followers were hoping the pop icon would mark the milestone anniversary of the release of her number one track, but they were left disappointed when they realised she had decided to lay low for a while. Earlier this month, she revealed in a since-deleted post that she wouldn’t b…