[PowerPC] Remove itinerary IIC_LdStDCBA (#207227)
The itinerary IIC_LdStDCBA is defined and used in scheduling models, but
no instruction is assigned to it. However, since the instruction is
basically retired (not part of the portable Power ISA), and all
scheduling models model it similar to IIC_LdStDCBF, the itinerary can be
removed.
