Clean release notes formatting

This will be rendered by GitHub releases, which preserves new lines, so
it looks better if we don't manually wrap.

Also remove placeholders, as the release will happen soon and will not
get new features or content for the currently empty sections.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Author: llucax

RELEASE_NOTES.md

@@ -1,28 +1,10 @@
 # Dispatch Highlevel Interface Release Notes
 
-## Summary
-
-<!-- Here goes a general summary of what this release is about -->
-
-## Upgrading
-
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
-
-## New Features
-
-<!-- Here goes the main new features and examples or instructions on how to use them -->
-
 ## Enhancements
 
 - Improved docstring documentation across the project.
 
 ## Bug Fixes
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
-
-* Fixed documentation cross-references to dependencies by updating the
-  mkdocstrings inventories to match the minimum dependency versions and
-  adding the missing `frequenz-client-base` inventory.
-* Declared the missing direct dependencies `frequenz-client-common`,
-  `frequenz-core` and `grpcio`, which were previously only pulled in
-  indirectly through `frequenz-client-dispatch`.
+* Fixed documentation cross-references to dependencies by updating the mkdocstrings inventories to match the minimum dependency versions and adding the missing `frequenz-client-base` inventory.
+* Declared the missing direct dependencies `frequenz-client-common`, `frequenz-core` and `grpcio`, which were previously only pulled in indirectly through `frequenz-client-dispatch`.