target/i386/emulate: remove flags_mask

The field is written but never read.

Cc: Wei Liu <liuwe@linux.microsoft.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/emulate/x86_decode.h

@@ -295,8 +295,6 @@ typedef struct x86_decode {
     struct x86_modrm modrm;
     struct x86_decode_op op[4];
     bool is_fpu;
-    uint32_t flags_mask;
-
 } x86_decode;
 
 uint64_t sign(uint64_t val, int size);