[firebase-release] Removed change log and reset repo after 13.21.0 re…

…lease

CHANGELOG.md

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-- Add apphosting:rollouts:create CLI command. (#7687)
-- Updated emulator UI to version 1.14.0, which adds support for SDK defined extensions.
-- Added emulator support for SDK defined extensions.
-- Fixed various trigger handling issues in the Functions emualtor, including an issue where Eventarc functions would not be emulated correctly after a reload.
-- Added support for generating Dart SDKs for Data Connect connectors.
-- Commands now correctly default to 'default' alias when there is more than one alias listed. (#7624)
-- Updated Data Connect emulator to v1.15.0, which includes bug fixes for `insertMany` and improved error handling.