x86/build/vdso: Remove unused $(vobjs-nox32) in Makefile

Since commit bfad381c

 ("x86/vdso: Improve the fake section
headers"), $(vobjs-nox32) is empty.  Therefore, $(vobjs64-for-x32)
is the same as $(vobjs-y).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1526352744-28229-2-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>