arch: Delete now unused operand types. These have been subsumed into the RegOperand type, and are fronted by the *RegOperandDesc OperandDesc classes. Change-Id: If57b683b06f3002004863c2d74f2a645882fbd41 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49734 Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com> Tested-by: kokoro <noreply+kokoro@google.com>