x86: stop exporting msr-index.h to userland

Even if this file was not in an uapi directory, it was exported because
it was listed in the Kbuild file.

Fixes: b72e7464 ("x86/uapi: Do not export <asm/msr-index.h> as part of the user API headers")
Suggested-by: NBorislav Petkov <bp@alien8.de>
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: NIngo Molnar <mingo@kernel.org>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

arch/x86/include/uapi/asm/Kbuild

@@ -27,7 +27,6 @@ header-y += ldt.h
 header-y += mce.h
 header-y += mman.h
 header-y += msgbuf.h
-header-y += msr-index.h
 header-y += msr.h
 header-y += mtrr.h
 header-y += param.h