hw/timer/hpet: Drop the unused macro

HPET_TN_CFG_BITS_READONLY_OR_RESERVED is not used in any place since
HPET_TN_CFG_WRITE_MASK has been already used to check and fix the
writable bits in hpet_ram_write().

Drop this unused macro.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

include/hw/timer/hpet.h

@@ -58,7 +58,6 @@
 #define HPET_TN_CFG_WRITE_MASK  0x7f4e
 #define HPET_TN_INT_ROUTE_SHIFT      9
 #define HPET_TN_INT_ROUTE_CAP_SHIFT 32
-#define HPET_TN_CFG_BITS_READONLY_OR_RESERVED 0xffff80b1U
 
 struct hpet_fw_entry
 {