add NEWS about OldPkg moving out of the julia repo

Author: KristofferC

NEWS.md

@@ -19,5 +19,11 @@ Compiler/Runtime improvements
 Deprecated or removed
 ---------------------
 
+The old package manager (now called `OldPkg`) has been moved to a
+separate repository at https://github.com/JuliaArchive/OldPkg.jl ([#27930])
+
 Command-line option changes
 ---------------------------
+
+<!--- generated by NEWS-update.jl: -->
+[#27930]: https://github.com/JuliaLang/julia/issues/27930