aarch64: Reduce the size of register_context

We don't need to store 32 general and vector registers.
Only 8 of each are used for parameter passing.

src/aarch64/ffitarget.h

@@ -54,10 +54,4 @@ typedef enum ffi_abi
 #define FFI_EXTRA_CIF_FIELDS unsigned aarch64_flags
 #endif
 
-#define AARCH64_FFI_WITH_V_BIT 0
-
-#define AARCH64_N_XREG 32
-#define AARCH64_N_VREG 32
-#define AARCH64_CALL_CONTEXT_SIZE (AARCH64_N_XREG * 8 + AARCH64_N_VREG * 16)
-
 #endif