[gn] port 40c45b6 more (rm clang-rename)

40c45b6 already removed most traces of clang-rename from the
GN build (thanks!), but it didn't delete the build file for unit tests.

Author: nico

llvm/utils/gn/secondary/clang/unittests/BUILD.gn

@@ -16,7 +16,6 @@ group("unittests") {
     "InstallAPI:InstallAPITests",
     "Interpreter:ClangReplInterpreterTests",
     "Lex:LexTests",
-    "Rename:ClangRenameTests",
     "Rewrite:RewriteTests",
     "Sema:SemaTests",
     "Serialization:SerializationTests",