x86/vdso: Remove hpet_page from vDSO

This trivial cleanup finalizes the removal of vDSO HPET support.

Fixes: 1ed95e52 ("x86/vdso: Remove direct HPET access through the vDSO")
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: luto@kernel.org
Cc: bp@alien8.de
Link: https://lkml.kernel.org/r/20190401114045.7280-1-zhang.jia@linux.alibaba.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>