Update headers.

This should be marked as implemented in Swift 6.2, and you no longer
want to look at the `_Backtracing` module.

Author: al45tair

proposals/0419-backtrace-api.md

@@ -3,8 +3,7 @@
 * Proposal: [SE-0419](0419-backtrace-api.md)
 * Authors: [Alastair Houghton](https://github.com/al45tair)
 * Review Manager: [Steve Canon](https://github.com/stephentyrone)
-* Status: **Accepted**
-* Implementation: Implemented on main, requires explicit `_Backtracing` import.
+* Status: **Implemented (Swift 6.2)**
 * Review: ([pitch](https://forums.swift.org/t/pitch-swift-backtracing-api/62741)) ([review](https://forums.swift.org/t/se-0419-swift-backtracing-api/69595)) ([acceptance](https://forums.swift.org/t/accepted-with-modifications-se-0419-swift-backtracing-api/70318))
 
 ## Introduction