Normalize SE-0409 upcoming feature flag (#2439)

* Normalize SE-0409 upcoming feature flag

The upcoming feature flag is now no longer always enabled in
Swift 6 language mode. Since it is always enabled in a future
unannounced version of Swift, it should have no annotation.

Also the UFF field should not include a summary of the effects
of the flag.

* Update status to 'Implemented (Swift 6.0)'

Author: dempseyatgithub

proposals/0409-access-level-on-imports.md

@@ -3,9 +3,9 @@
 * Proposal: [SE-0409](0409-access-level-on-imports.md)
 * Author: [Alexis Laferrière](https://github.com/xymus)
 * Review Manager: [Frederick Kellison-Linn](https://github.com/Jumhyn)
-* Status: **Accepted with modifications**
+* Status: **Implemented (Swift 6.0)**
 * Implementation: On main and release/5.9 gated behind the frontend flag `-enable-experimental-feature AccessLevelOnImport`
-* Upcoming Feature Flag: `InternalImportsByDefault` (Enables Swift 6 behavior with imports defaulting to internal. Soon on main only.)
+* Upcoming Feature Flag: `InternalImportsByDefault`
 * Review: ([pitch](https://forums.swift.org/t/pitch-access-level-on-import-statements/66657)) ([review](https://forums.swift.org/t/se-0409-access-level-modifiers-on-import-declarations/67290)) ([acceptance](https://forums.swift.org/t/accepted-with-modifications-se-0409-access-level-modifiers-on-import-declarations/67666))
 
 ## Introduction