[gn build] Port 6cbc373

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/src/BUILD.gn

@@ -149,7 +149,6 @@ cxx_sources = [
   "ios.cpp",
   "ios.instantiations.cpp",
   "iostream.cpp",
-  "legacy_pointer_safety.cpp",
   "locale.cpp",
   "memory.cpp",
   "memory_resource.cpp",