tests/test-char: Remove unused "chardev/char-mux.h" include

This test never required "chardev/char-mux.h", remove it.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200423202112.644-3-philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

tests/test-char.c

@@ -6,7 +6,6 @@
 #include "qemu/option.h"
 #include "qemu/sockets.h"
 #include "chardev/char-fe.h"
-#include "chardev/char-mux.h"
 #include "sysemu/sysemu.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-char.h"