Don't link stdlibUnitTest against the _Distributed library.

We don't use anything from the _Distributed library, and linking it makes
back-deployment testing for _Concurrency harder.

Author: DougGregor

stdlib/private/StdlibUnittest/CMakeLists.txt

@@ -16,9 +16,6 @@ if (SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY)
   list(APPEND swift_stdlib_unittest_link_libraries "swift_Concurrency")
   list(APPEND swift_stdlib_unittest_modules "_Concurrency")
 endif()
-if (SWIFT_ENABLE_EXPERIMENTAL_DISTRIBUTED)
-  list(APPEND swift_stdlib_unittest_link_libraries "swift_Distributed")
-endif()
 
 add_swift_target_library(swiftStdlibUnittest ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STDLIB
   # This file should be listed the first.  Module name is inferred from the