Remove duplicated commons-io dep

It seems like having it as a compile dependency already works for the
tests. Having it duplicated seems to sometimes trigger errors (e.g. a
user reported a duplicate zip entry due to the duplication) and might
also be problematic if we don't keep the two versions in sync.

app/build.gradle

@@ -28,8 +28,6 @@ dependencies {
     }
     compile 'io.reactivex:rxjava:1.1.0'
     compile 'io.reactivex:rxandroid:0.23.0'
-
-    androidTestCompile 'commons-io:commons-io:2.4'
 }
 
 if (!hasProperty('sourceDeps')) {