Deduplicate RELEASE_NOTES and Releases list

I looked at `RELEASE_NOTES.md` for information about the latest releases and was confused by their absence. Then I found all the notes in the GitHub Releases page. This PR suggests using the Releases list as the sole source of release notes.

Author: davidtheclark

RELEASE_NOTES.md

@@ -1,18 +1,3 @@
 # Release Notes
 
-## v1.1.1
-
-- Fixed TCP Client Memory Leak (#32 via #34). Thanks @davidtheclark!
-
-## v1.1.0
-
-- Preserve the logger context across flushes
-- Merge duplicate dimension sets
-- Add environment override and LocalEnvironment
-- Make LogGroup optional for DefaultEnvironment
-- Set Max Dimensions = 9
-- Support more than 100 metrics transparently
-
-## v1.0.0
-
-Initial release
+See the repository's [Releases list](https://github.com/awslabs/aws-embedded-metrics-node/releases).