[iOS/ARC] Fix a violation of ODR in base::BindBlock under ARC.

base/mac/scoped_nsobject_unittest_arc.mm

Index: base/mac/scoped_nsobject_unittest_arc.mm
diff --git a/base/mac/scoped_nsobject_unittest_arc.mm b/base/mac/scoped_nsobject_unittest_arc.mm
index 1f69c5640670d6e1d7451b0c8ebd366213be92c3..5cbf3f83833effc65eba1f4db8bc03f50528f262 100644
--- a/base/mac/scoped_nsobject_unittest_arc.mm
+++ b/base/mac/scoped_nsobject_unittest_arc.mm
@@ -14,12 +14,6 @@
 #error "This file requires ARC support."
 #endif
 
-// This free-function is there to ensure that the object file in not discarded
-// at link time when building with gyp (it is required because targets is built
-// as a static library with gyp and not source set which cause the object file
-// to be discarded if no symbol is used). Remove once gyp support is dropped.
-void ScopedNSObjectUnittestArcLinkerWorkaround() {}
-
 namespace {
 
 template <typename NST>