It’s been proven again and again: Art thrives on restriction. And kitschy art demands it the way even the most genteel of man-bat hybrids demand hot, fresh blood. So it’s no surprise that the best thing about Landless Theatre Company’s current revival of Bat Boy: The Musical is its audacious modesty. That’s not an oxymoron: Their production is low-budget, low-tech, low-brow, and high camp. One wishes it was a bit more high-efficiency: No show…