drivers/intel: remove unused header series6.h

Last usage of this header was in beltino platform, which is now
deleted.

BUG=chromium:990438
TEST=compiles

Change-Id: I6138d1ef3f192223ae291a8a476907deb8aa1ef0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/2392520
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Auto-Submit: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>
1 file changed