x86: msr-index.h remove duplicate MSR C001_0015 declaration

MSRC001_0015 Hardware Configuration Register (HWCR) is already defined
as MSR_K7_HWCR.

And HWCR is available for >= K7.

So MSR_K8_HWCR is not required and no-one is using it.

[ Impact: cleanup, no object code change ]

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>