[firebase-release] Removed change log and reset repo after 15.8.0 release

Author: google-oss-bot

CHANGELOG.md

@@ -1,5 +0,0 @@
-- Corrects issue with updateService in runv2.ts (#9918)
-- Updated suite of MCP tools for Firestore to include many new tools. Firestore tools no longer support emulator mode.
-- Updated the Firebase Data Connect local toolkit to v3.2.0, which includes the following changes: (#9975)
-  - Support for uuidV7()
-  - Support for custom PostgreSQL schema names.