Removes an unused library from build.gradle.

app/build.gradle

@@ -46,7 +46,6 @@ dependencies {
     compile 'com.android.support:support-v13:25.3.1'
     compile 'com.android.support:design:25.3.1'
     compile 'com.android.support:exifinterface:25.3.1'
-    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha7'
     compile 'com.squareup.retrofit2:retrofit:2.2.0'
     compile 'com.squareup.retrofit2:converter-gson:2.2.0'
     compile 'com.squareup.picasso:picasso:2.5.2'