Don't ProGuard debug builds
Don't ProGuard debug builds

This patch removes the ProGuard step from debug builds. ProGuarding
scratch debug builds some how runs faster than not[0]. However, it
greatly increases incremental build times which is the most common use
case.

[0] https://gerrit.wikimedia.org/r/#/c/251981/1/app/build.gradle

Change-Id: I935d5e7ec54f40896cb199b3c859d70eccf03563

anirudh24seven/apps-android-wikipedia,carloshwa/apps-android-wikipedia,dbrant/apps-android-wikipedia,carloshwa/apps-android-wikipedia,dbrant/apps-android-wikipedia,anirudh24seven/apps-android-wikipedia,wikimedia/apps-android-wikipedia,SAGROUP2/apps-android-wikipedia,SAGROUP2/apps-android-wikipedia,Duct-and-rice/KrswtkhrWiki4Android,anirudh24seven/apps-android-wikipedia,Duct-and-rice/KrswtkhrWiki4Android,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,Duct-and-rice/KrswtkhrWiki4Android,wikimedia/apps-android-wikipedia,anirudh24seven/apps-android-wikipedia,SAGROUP2/apps-android-wikipedia,wikimedia/apps-android-wikipedia,carloshwa/apps-android-wikipedia,SAGROUP2/apps-android-wikipedia,Duct-and-rice/KrswtkhrWiki4Android,carloshwa/apps-android-wikipedia,dbrant/apps-android-wikipedia,carloshwa/apps-android-wikipedia,dbrant/apps-android-wikipedia,SAGROUP2/apps-android-wikipedia,Duct-and-rice/KrswtkhrWiki4Android,anirudh24seven/apps-android-wikipedia