Prune uses library classes even without profile

The previous pruning relied on the classes being pruned from the
profile, and then using the profile to prune classes. If there was
no profile, the uses library classes were incorrectly left unpruned.

Leaving these classes unpruned caused aborts during compilation.

Bug: 30688277

Test: adb shell dex2oat --runtime-arg -classpath --runtime-arg /system/framework/com.google.android.maps.jar --dex-file=/data/app/comb.BBClient-1/base.apk --dex-location=/data/app/comb.BBClient-1/base.apk --oat-file=/data/app/comb.BBClient-1/oat/arm/base.odex  --app-image-file=/data/app/comb.BBClient-1/oat/arm/base.art --image-format=lz4 --compiler-filter=speed

Change-Id: I261b8894847b5b0a4f7330f49666e823a1b38bb0