Small cleanups

This change addresses several cleanup opportunities that came up during
https://r.android.com/1298080, including:

* Remove --no-dex2oat from the run-test usage message, since this option
  is no longer supported.

* Refactor the `b ? OatHeader::kTrueValue : OatHeader::kFalseValue`
  pattern in dex2oat so there is less code duplication.

Test: ./test.py --host
Change-Id: I9a2a6649116cd431c3829901965f2e48812fcbd6
2 files changed