msm: Remove unused file core.h

Commit be2109e1 removed the usage
of core.h. Remove the file as well.

    commit be2109e1
    Author: David Brown <davidb@codeaurora.org>
    Date:   Wed Sep 12 16:01:40 2012 -0700

        ARM: msm: Move core.h contents into common.h
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
[davidb: Clarify commit text with mentioned commit]
Signed-off-by: David Brown <davidb@codeaurora.org>

arch/arm/mach-msm/core.h

-extern struct smp_operations msm_smp_ops;
-extern void msm_cpu_die(unsigned int cpu);