[clangd] Replace UniqueFunction with llvm::unique_function.

One implementation of this ought to be enough for everyone.

llvm-svn: 336228
diff --git a/clang-tools-extra/unittests/clangd/SyncAPI.cpp b/clang-tools-extra/unittests/clangd/SyncAPI.cpp
index 6b773fa..fa4f376 100644
--- a/clang-tools-extra/unittests/clangd/SyncAPI.cpp
+++ b/clang-tools-extra/unittests/clangd/SyncAPI.cpp
@@ -36,7 +36,7 @@
   }
   CaptureProxy &operator=(CaptureProxy &&) = delete;
 
-  operator UniqueFunction<void(T)>() && {
+  operator llvm::unique_function<void(T)>() && {
     assert(!Future.valid() && "conversion to callback called multiple times");
     Future = Promise.get_future();
     return Bind(