APC-Rewrite AI fix.

Before:  AI's on new APC system would constantly add more and more power usage to the APC

After:   AI's no longer handle their power consumption, that has been pushed off to an /obj/machinery/ai_powersupply dummy object which will process the power usage.  This is much cleaner because machinery objects are already processed properly for the new system and keeps us from having to rewrite a bunch of AI code to bring the AI in line with how the new APC system works.
Merge pull request #4581 from Ccomp5950/ai_apc_fix

APC-Rewrite AI fix.