We don't really need to track this fd beyond the initial creation of
the socket. We already know if the system has been initialised by
virtue of the gdbserver_state so lets remove it. This makes the later
re-factoring easier.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200430190122.4592-6-alex.bennee@linaro.org>