Disable Renovate

We have decided to retire Distribution Viewer, so there's no reason for
Renovate to upgrade packages right now. If we revive Distribution Viewer
at some point in the future, we can re-enable it.

More information about the decision to retire Distribution Viewer can be
found here:

https://bugzilla.mozilla.org/show_bug.cgi?id=1461371

renovate.json

@@ -1,4 +1,5 @@
 {
+    "enabled": false,
     "extends": [
         "config:base"
     ],