Erling Haaland believes he is ‘finally’ getting back to his full fitness. Manchester City returned to their free-scoring best after two narrow 1-0 wins in succession by destroying Luton Town 6-2 on Tuesday. The emphatic victory sees Pep Guardiola’s side advance to the FA Cup quarter-finals and take another step closer to winning a remarkable back-to-back treble. Kevin De Bruyne rightly earned plenty of plaudits for creating four of the goals and Mateo Kovacic scored a beauty but Erling Haaland was the star of the show. The Norwegian sensation obliterated the Luton defence and scored five times…