virt: acrn: Remove unsued acrn_irqfds_mutex.

acrn_irqfds_mutex is not used, never was.

Remove acrn_irqfds_mutex.

Fixes: aa3b483f ("virt: acrn: Introduce irqfd")
Cc: Fei Li <fei1.li@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/YidLo57Kw/u/cpA5@linutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/virt/acrn/irqfd.c

@@ -17,7 +17,6 @@
 #include "acrn_drv.h"
 
 static LIST_HEAD(acrn_irqfd_clients);
-static DEFINE_MUTEX(acrn_irqfds_mutex);
 
 /**
  * struct hsm_irqfd - Properties of HSM irqfd