Remove unused/not working function tracing flag and functionality.

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
===================================================================
--- runtime/vm/stub_code_x64.cc	(revision 14749)
+++ runtime/vm/stub_code_x64.cc	(working copy)
@@ -2030,6 +2030,20 @@
   __ jmp(&compute_result, Assembler::kNearJump);
 }
 
+// Calls to runtime to ooptimized give function
+// RDX: function to be reoptimized.
+// RAX: result of function being optimized (preserved).
+void StubCode::GenerateOptimizeFunctionStub(Assembler* assembler) {
+  AssemblerMacros::EnterStubFrame(assembler);
+  __ pushq(RAX);
+  __ pushq(RDX);
+  __ CallRuntime(kOptimizeInvokedFunctionRuntimeEntry);
+  __ popq(RDX);
+  __ popq(RAX);
+  __ LeaveFrame();
+  __ ret();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64