pci: remove irq_dev

Unused.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

kern/arch/x86/pci.h

diff --git a/kern/arch/x86/pci.h b/kern/arch/x86/pci.h
index 88bdd00..a9e50a3 100644
--- a/kern/arch/x86/pci.h
+++ b/kern/arch/x86/pci.h
@@ -169,7 +169,6 @@
 
 struct pci_device {
 	STAILQ_ENTRY(pci_device)	all_dev; /* list of all devices */
-	SLIST_ENTRY(pci_device)		irq_dev; /* list of all devs on irq */
 	char				name[9];
 	spinlock_t			lock;
 	uintptr_t			mmio_cfg;