Do not use npic image for oat file assistant tests.

Because patchoat will no longer support relocating npic images.
All that matters for the oat file assistant test is that the secondary
boot image has a different checksum than the primary one.

Bug: 33192586
Test: oat_file_assistant_test
Change-Id: I7ece86337221a9d0c56534b2045026ba5d3d7d89
3 files changed