Fix USE_D8 in conjunction with USE_D8_BY_DEFAULT

We can no longer use DX=dx. Instead, we can just set USE_D8=false
after that USE_D8_BY_DEFAULT change.

Bug: 67569208
Test: ./art/test.py --host
Change-Id: Ic48157e6a26acc1380fc5ef40076d4e3b65c2b79
22 files changed