Skip "verify" packages in otapreopt.

Since http://r.android.com/1590077, the runtime is able to use the vdex
files even if the dependencies have changed. There is no more need to
re-generate the vdex files.

Bug: 199756868
Test: Run system/update_engine/scripts/update_device.py on a clean Pixel
  5 device and see that the time spent on the otapreopt step went down
  from 7 minutes to 2.5 minutes.
Change-Id: I455554ad905ec3513ce1fd4e5d209a43fa27dbac