powerpc/64s/exception: Remove unused SOFTEN_VALUE_0x980

Remove SOFTEN_VALUE_0x980, it's been unused since commit
dabe859e ("powerpc: Give hypervisor decrementer interrupts their
own handler") (Sep 2012).
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/exception-64s.h

@@ -583,7 +583,6 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 /* This associate vector numbers with bits in paca->irq_happened */
 #define SOFTEN_VALUE_0x500	PACA_IRQ_EE
 #define SOFTEN_VALUE_0x900	PACA_IRQ_DEC
-#define SOFTEN_VALUE_0x980	PACA_IRQ_DEC
 #define SOFTEN_VALUE_0xa00	PACA_IRQ_DBELL
 #define SOFTEN_VALUE_0xe80	PACA_IRQ_DBELL
 #define SOFTEN_VALUE_0xe60	PACA_IRQ_HMI