x86, pvclock: Remove leftover scale_delta() function

Commit 92580d64e16402762e2acc3022f065397c780425
("x86: pvclock: Move scale_delta into common header")
forgot to remove scale_delta.

Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
Cc: Zachary Amsden <zamsden@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Glauber Costa <glommer@redhat.com>
LKML-Reference: <20101105110444.BAF6D6FC03B@msa105.auone-net.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>