boards: qemu_nios2: drop board definition

Remove qemu_nios2, more removals will follow.

Part of #89280

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Author: nashif

boards/qemu/nios2/Kconfig

@@ -282,7 +282,7 @@ elseif(QEMU_NET_STACK)
   endif()
 endif(QEMU_PIPE_STACK)
 
-if(CONFIG_CAN AND NOT (CONFIG_NIOS2 OR CONFIG_SOC_LEON3))
+if(CONFIG_CAN AND NOT (CONFIG_SOC_LEON3))
   # Add CAN bus 0
   list(APPEND QEMU_FLAGS -object can-bus,id=canbus0)