Revert "Merge pull request swiftlang#59227 from al45tair/pr/fix-bd-concurrency-2"

This reverts commit 729f912, reversing
changes made to b7fd963.

Author: ahoppen

stdlib/public/BackDeployConcurrency/CMakeLists.txt

@@ -66,4 +66,4 @@ set(LLVM_OPTIONAL_SOURCES
   TaskSleepDuration.swift)
 
 add_subdirectory(../Concurrency stdlib/public/BackDeployConcurrency)
-add_subdirectory(../Threading)
+add_subdirectory(../Threading stdlib/public/BackDeployConcurrency)