ART-tests: remove DX-dependency from 566-checker-signum

One test case converts a boolean to 0/1 with a conditional. This construct
is optimized away by D8. This CL moves this test case to smali and enables
D8.

Test: art/test.py -b -r --host -t 566-checker-signum
      Tested locally with --target/--gcstress
Bug: 65168732

Change-Id: Ic1f901dea486692174d38281413fe06539a41a34