target/rx: Ensure not being build on user emulation Currently only system emulation is supported. Assert no target code is built for user emulation. Remove #ifdef'ry since more work is required before being able to emulate a user process. Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-Id: <20250121142341.17001-3-philmd@linaro.org>