Dramatic new video shows a strap-hanger taking matters into his own hands, pinning down an unhinged man in a deadly incident at a Manhattan subway station this week. The 24-year-old passenger stepped in after the vagrant, identified by sources as Jordan Neely, 30, began going on an aggressive rant on a northbound F train Monday afternoon, according to police and a witness who took the video. “He starts to make a speech,” freelance journalist Juan Alberto Vazquez said in Spanish during an interview Tuesday, referring to the disturbed man. “He started screaming in an aggressive manner,” Vazquez told The Post....