x86/vector: Remove the unused macro FPU_IRQ

The macro FPU_IRQ has never been used since v3.10, So remove it.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20180426060832.27312-1-douly.fnst@cn.fujitsu.com