[firebase-release] Removed change log and reset repo after 3.1.0 release

Author: firebase-ops

changelog.txt

@@ -1,6 +0,0 @@
-feature - Adds privacyPolicyUrl config to enable developers to provide privacy policy URL. And shows Term of Service and Privacy Policy link on every screen for GDPR compliance.
-feature - Defines the FirebaseUI externs.
-feature - Defines the typescript definitions.
-feature - Optimizes sign in flow to use updateCurentUser eliminating 2 RPCs in the process.
-fixed - Catches errors that occur due to incompatible versions of firebase.js being used with firebaseui.js.
-fixed - Fixes reCAPTCHA invisible badge which was getting hidden.