[firebase-release] Removed change log and reset repo after 15.18.0 release

Author: google-oss-bot

CHANGELOG.md

@@ -1,9 +0,0 @@
-- Updated Pub/Sub emulator to version 0.8.31
-- Resolves undefined regions earlier, during the build to backend resolution phase (#10471)
-- Updated the Firebase Data Connect local toolkit to v3.4.8, which includes the following changes:
-  - Fixed an issue in Dart code generation where nullable BigInt was not handled correctly.
-  - Added support for nested 1:Many relational batch mutations.
-  - Updated the Golang dependency version to 1.25.10.
-- Default timeout for Dart functions is now 60 seconds when not explicitly set (#10501)
-- Support secret environment variables for Cloud Run functions (#10489)
-- Set requiredProjectBindings in AI Logic services (#10503)