Constraint Layout beta 5 is the release candidate, and added a lint to deprecate older versions.
The easiest way to get rid of the lint error is to press Alt-Enter and choose the first option to upgrade.
However, I encountered a bug, which forces me to stay with beta4 until the next version comes out with the fix. I still want to get rid of the lint error so my continuous build does not fail. I didn't want to change lintOptions abortOnError to false in build.gradle because I still want my build to catch other fatal lint errors.
I tried to get Android Studio to fix this lint error for me by choosing Disable inspection from Alt-Enter. Alas, that only changed the local settings. Turns out that I need to go to Settings → Editor → Inspections to undo that.
The option I wanted is Suppress: Add tools:ignore="MissingConstraints" attribute, which modifies the xml for me to add the appropriate lint suppression.
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:ignore="MissingConstraints"> <!-- Cannot upgrade to beta5 due to http://b.android.com/233863 -->
Finally, I added a comment to remind me why I suppress the lint error.
More info: Suppress Lint Warnings.