hvf: arm: Remove PL1_WRITE_MASK

As it had never been used since the first commit a1477da ("hvf: Add
Apple Silicon support").

Signed-off-by: Zenghui Yu <zenghui.yu@linux.dev>
Message-id: 20240422092715.71973-1-zenghui.yu@linux.dev
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/hvf/hvf.c

@@ -150,7 +150,6 @@ void hvf_arm_init_debug(void)
 
 #define HVF_SYSREG(crn, crm, op0, op1, op2) \
         ENCODE_AA64_CP_REG(CP_REG_ARM64_SYSREG_CP, crn, crm, op0, op1, op2)
-#define PL1_WRITE_MASK 0x4
 
 #define SYSREG_OP0_SHIFT      20
 #define SYSREG_OP0_MASK       0x3