Prune Release Notes for 5.10 GA

[sbrannen]

Deliverables

• Merge the release notes for 5.10 M1 and RC1.
• Ensure that release note entries which address changes between M1 and RC1 are removed or, if applicable, that each entry for a change in RC1 is merged into the original corresponding entry for M1.

[marcphilipp]

Reverted in 2c278c7 for the 5.10.0-RC2 release