Revert "[gn build] port d1d36f7ad (llvm-tapi-diff)"

This reverts commit 13155138c1.
d1d36f7ad was reverted in 5337c7550d.

llvm/utils/gn/secondary/llvm/test/BUILD.gn

@@ -273,7 +273,6 @@ group("test") {
     "//llvm/tools/llvm-split",
     "//llvm/tools/llvm-strings",
     "//llvm/tools/llvm-symbolizer:symlinks",
-    "//llvm/tools/llvm-tapi-diff",
     "//llvm/tools/llvm-undname",
     "//llvm/tools/llvm-xray",
     "//llvm/tools/lto",

llvm/utils/gn/secondary/llvm/tools/llvm-tapi-diff/BUILD.gn

@@ -1,11 +0,0 @@
-executable("llvm-tapi-diff") {
-  deps = [
-    "//llvm/lib/Object",
-    "//llvm/lib/Support",
-    "//llvm/lib/TextAPI",
-  ]
-  sources = [
-    "llvm-tapi-diff.cpp",
-    "DiffEngine.cpp",
-  ]
-}