Is it déjà vu, or just a Mirage? The embattled former site of the Brooklyn Mirage open-air music venue faces yet another race against time — after the “unsafe” structure from last year’s failed opening caused delays for the pricey new nightclub taking over, The Post has learned. Pacha New York is taking over the space formerly known as the Brooklyn Mirage. Pacha New York FIVE Holdings, the East Williamsburg venue’s new Dubai-based operator , is set to open the seasonal nightclub at 140 Stewart Ave. as Pacha New York by mid-June, and confirmed to The Post it is building a massive stage elsewhere to speed up the process. The Brooklyn Mirage successor is already peddling $150 tickets for its opening weekend — a massive increase over the $20 starting price that the Mirage was known for. Work on the venue’s platform and supports has been underway “off-site” since January, a Pacha New York rep said.…