The best way to help a struggling public school is to cannibalize it.     At least that’s what Betsy DeVos thinks – and so does her Pennsylvania puppet Mike Turzai.     The Republican Speaker of the state House is expected to propose a school voucher bill Monday that will treat Harrisburg Schools as nothing more than carrion fit for plunder by school privatization vultures.     Sure the district is in state receivership after decades of neglect and…