Update CHANGELOG.md

Author: Borda

CHANGELOG.md

@@ -4,9 +4,6 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
-## Metrics (will be added to unreleased once the metric branch was finished)
-- Add Metric Base Classes ([#1326](https://github.com/PyTorchLightning/pytorch-lightning/pull/1326))
-
 ## [unreleased] - YYYY-MM-DD
 
 ### Added