x86/vdso: Delete vvar.h

All users have been removed.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241010-vdso-generic-base-v1-19-b64f0842d512@linutronix.de

Author: t-8ch