hw/arm/xlnx-zynqmp: Remove obsolete 'has_rpu' property

hw/arm/xlnx-zynqmp: Remove obsolete 'has_rpu' property

We hint the 'has_rpu' property is no longer required since commit
6908ec448b4 ("xlnx-zynqmp: Properly support the smp command line
option") which was released in QEMU v2.11.0.

Beside, this device is marked 'user_creatable = false', so the
only thing that could be setting the property is the board code
that creates the device.

Since the property is not user-facing, we can remove it without
going through the deprecation process.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210219144350.1979905-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>