The NYPD bomb squad was probing a suspicious item near Gracie Mansion and evacuated an adjacent park Tuesday, just four days after thwarting a terror attack there — later discovering the package was a container wrapped with camouflage tape and full of liquid and not posing an immediate threat, law-enforcement sources said. Cops responded to East 86th Street near East End Avenue on the Upper East Side in Manhattan around midday after reports of a suspect container on the promenade there, law