[firebase-release] Removed change log and reset repo after 7.2.3 release

CHANGELOG.md

@@ -1,8 +0,0 @@
-* Introduce experimental support for browser clients to the Firestore emulator.
-* No longer require authentication to run the functions emulator.
-* Add new project management commands: `projects:create`, `projects:list`,
-  `projects:addFirebase`.
-* Add new app management commands: `apps:create`, `apps:list`, `apps:sdkconfig`.
-* Improve `init` command to be able to create a new project.
-* Automatically choose a port for the Firestore emulator to serve WebChannel traffic.
-* Add support for running queries inside of transactions to the Firestore emulator.