B #-: Remove obsolete secondary platform notes (#3203)

(cherry picked from commit 717ad10)

Author: xorel

source/intro_release_notes/release_notes/index.rst

@@ -9,7 +9,6 @@ Release Notes |version|
 
    What's New <whats_new>
    Platform Notes <platform_notes>
-   Secondary Platforms <secondary>
    Compatibility Guide <compatibility>
    Known Issues <known_issues>
    Acknowledgements <acknowledgements>