x86/asm: Remove unused L3_PAGE_OFFSET

L3_PAGE_OFFSET was introduced in commit a6523748 (paravirt/x86, 64-bit: move
__PAGE_OFFSET to leave a space for hypervisor), but has no users.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Link: http://lkml.kernel.org/r/1453810881-30622-1-git-send-email-kuleshovmail@gmail.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>