Convert zipr unpin plugin to use IRDB unpinned IBT IR method
Previous attempts at unpinning used a relocation hung on the instruction indicating that an unpin should occur at Zipr time.
A better method is to set the IBTA to 0. Current IR models already use this method for marking return points as unpinned IBTs.
Idea: Convert IR builder (in sec-trans/libIRDB/tests) to use the IR unpin instead of adding the unpin relocations. Then, remove the unpin plugin.