Revert the DetId renumbering fix (when SLHC11/12 files no longer need to be read)

**Leave this sitting in the queue until SLHC11 files no longer need to be read**
This completely reverts the hack from #4714 that allows compatibility of files created with versions of CMSSW from before and after the pixel disc renumbering.

This shouldn't be applied until SLHC11 files (e.g. the Technical Proposal Phase 1 GEN-SIM samples) no longer need to be read.  The code of CMSSW_6_2_X_SLHC will no doubt change underneath while this is in the queue, but at lease there's a record of what needs to be changed if I fall under a bus.