RISC-V: Remove unused class definitions

Removes a whole lot of unnecessary boilerplate code. Machines
don't need to be objects. The expansion of the SOC object model
for the RISC-V machines will happen in the future as SiFive
plans to add their FE310 and FU540 SOCs to QEMU. However, it
seems that this present boilerplate is complete unnecessary.

Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: Michael Clark <mjc@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

include/hw/riscv/virt.h

@@ -19,10 +19,6 @@
 #ifndef HW_VIRT_H
 #define HW_VIRT_H
 
-#define TYPE_RISCV_VIRT_BOARD "riscv.virt"
-#define VIRT(obj) \
-    OBJECT_CHECK(RISCVVirtState, (obj), TYPE_RISCV_VIRT_BOARD)
-
 typedef struct {
     /*< private >*/
     SysBusDevice parent_obj;
@@ -45,7 +41,6 @@ enum {
     VIRT_DRAM
 };
 
-
 enum {
     UART0_IRQ = 10,
     VIRTIO_IRQ = 1, /* 1 to 8 */