Hayley Mills skyrocketed to fame as a child star under Walt Disney’s wing for seven years — only to see her once-promising fortune slip away. The actress, whose most memorable roles included “Pollyanna” and “The Parent Trap,” recently appeared alongside her sister, Juliet Mills, on  “The Rosebud Podcast.”  The appearance celebrated Mills’ 80th birthday. When host Gyles Brandreth pressed Mills on what became of “the millions” she earned during her Disney years , she replied, “I gave it to the tax man.” “It was rather a big chunk,” she admitted. “It was most of it because it was all put into a trust fund, because super tax was 90% in those days, so they had to do something.” “I do know the background of this, and it’s partly because you were poorly advised,” said Brandreth. “But also, it was partly to do with the naïveté of your father, I think.…