Fix issue where app with oauth addon will not backup or uninstall

src/addons.js

@@ -146,6 +146,13 @@ var KNOWN_ADDONS = {
         backup: NOOP,
         restore: NOOP,
         clear: NOOP,
+    },
+    oauth: { // kept for backward compatibility. keep teardown for uninstall to work
+        setup: NOOP,
+        teardown: teardownOauth,
+        backup: NOOP,
+        restore: NOOP,
+        clear: NOOP,
     }
 };
 
@@ -1869,3 +1876,13 @@ function statusGraphite(callback) {
         });
     });
 }
+
+function teardownOauth(app, options, callback) {
+    assert.strictEqual(typeof app, 'object');
+    assert.strictEqual(typeof options, 'object');
+    assert.strictEqual(typeof callback, 'function');
+
+    debugApp(app, 'teardownOauth');
+
+    appdb.unsetAddonConfig(app.id, 'oauth', callback);
+}