Remove system-images files from the SDK

The system images distributed externally are created by a separate
set of rules than these. There are no known consumers of these
legacy system-image files.

This makes the SDK zip architecture-agnostic.

Bug: 205008975
Test: m sdk sdk_repo dist
Test: diff sdk zips from sdk_phone_arm64 and sdk_phone_x86 (no diff)
Change-Id: I7ba2eb244a5930721c82895cd2947a1d2aff63e2
6 files changed