Prepare for release v1.12.0 (#514)

Author: simonvoelcker

RELEASE_NOTES.md

@@ -1,9 +1,5 @@
 # Frequenz channels Release Notes
 
-## Summary
-
-<!-- Here goes a general summary of what this release is about -->
-
 ## Upgrading
 
 - The old `Broadcast` class is deprecated in favour of the new auto-closing `BroadcastChannel`.
@@ -13,7 +9,3 @@
 ## New Features
 
 - There's a new `BroadcastChannel`, which returns a broadcast sender and a broadcast receiver.  The channel is auto-closing, meaning when all the senders or all the receivers are closed, the channel is closed.
-
-## Bug Fixes
-
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->