A London judge on Friday dismissed a terrorism charge against a member of Kneecap, the Irish-language rap group that has landed in hot water over its onstage crusading against Israel and for the Palestinian cause, saying that prosecutors had not brought the charge “in the correct form” within the required timeline. In May, British prosecutors charged the rapper, Liam Óg Ó hAnnaidh, who goes by the stage name Mo Chara, on an accusation of displaying a flag of Hezbollah, the Lebanon-based militant group that violently opposes Israel. Britain considers Hezbollah a terrorist organization and bans the display of its symbols. Mr. Ó hAnnaidh, who was charged under the name Liam O’Hanna, has said in interviews that he picked up the flag at a concert last year without knowing what it was after an audience member threw it onstage. On Friday, Paul Goldspring, the presiding judge, agreed with arguments made by Mr. Ó hAnnaidh’s legal team at previous hearings that prosecutors had taken action outside the statute of limitations and that the charges had not been signed off by legal officials in time.