Fix dependency when switching between build variants with and without Proguard.

With this change, in a user build the dependency looks like:
package.apk -> progaurd.classes.dex -> ... -> proguard.classes.jar
While in an eng build:
package.apk -> noproguard.classes.dex -> ... -> noproguard.classes.jar

Because package.apk is product-specific and removed when switching between
user and eng builds, it can always be built with the correct and up-to-date .dex file.

Bug: 3022484

Change-Id: I3a732cb3e256f193088c294dc4a0573188283cb2