hw/remote/proxy: Remove dubious 'event_notifier-posix.c' include

hw/remote/proxy: Remove dubious 'event_notifier-posix.c' include

event_notifier-posix.c is registered in meson's util_ss[] source
set, which is built as libqemuutil.a.p library. Both tools and
system emulation binaries are linked with qemuutil, so there is
no point in including this source file.

Introduced in commit bd36adb8df ("multi-process: create IOHUB
object to handle irq").

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230606134913.93724-1-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>