x86/vdso: Remove unused file

commit da861e18 ("x86, vdso: Get rid of the fake section mechanism")
left this file behind; nothing is using it anymore.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Cc: luto@amacapital.net
Link: https://lkml.kernel.org/r/20180504175935.104085-1-jannh@google.com