[firebase-release] Removed change log and reset repo after 12.9.0 release

Author: google-oss-bot

CHANGELOG.md

@@ -1,7 +0,0 @@
-- Revert enabling preferRest by default to avoid performance degradations for some users (#6520).
-- Fix blocking functions in the emulator when using multiple codebases (#6504).
-- Add force flag call-out for bypassing prompts (#6506).
-- Fixed an issue where the functions emulator did not respect the `--log-verbosity` flag (#2859).
-- Add the ability to look for the default Hosting site via Hosting's API.
-- Add logic to create a Hosting site when one is not available in a project.
-- Add checks for the default Hosting site when one is assumed to exist.