Revert 246124 "gn: Fix clang plugin on ios."

This isn't correct for the iOS xcode builder.

> gn: Fix clang plugin on ios.
> 
> BUG=336491
> TBR=brettw@chromium.org
> 
> Review URL: https://codereview.chromium.org/144073003

TBR=thakis@chromium.org

Review URL: https://codereview.chromium.org/134923005

git-svn-id: http://src.chromium.org/svn/trunk/src/build@246146 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/clang/BUILD.gn

@@ -15,7 +15,7 @@ config("find_bad_constructs") {
       "-Xclang",
     ]
 
-    if (is_mac || is_ios) {
+    if (is_mac) {
       cflags += [ rebase_path(
         "//third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib",
         ".", root_build_dir) ]