Get rid of unused field has_compiled_code_ from the Isolate structure.

runtime/vm/precompiler.cc

Index: runtime/vm/precompiler.cc
diff --git a/runtime/vm/precompiler.cc b/runtime/vm/precompiler.cc
index d190d5a65be8e2cac93fe8df4410293dfcc3b460..56695811076117a3e6269ab199a1f80721c6dc0c 100644
--- a/runtime/vm/precompiler.cc
+++ b/runtime/vm/precompiler.cc
@@ -3497,8 +3497,6 @@ bool PrecompileParsedFunctionHelper::Compile(CompilationPipeline* pipeline) {
         ASSERT(thread()->IsMutatorThread());
         FinalizeCompilation(&assembler, &graph_compiler, flow_graph);
       }
-      // Mark that this isolate now has compiled code.
-      isolate()->set_has_compiled_code(true);
       // Exit the loop and the function with the correct result value.
       is_compiled = true;
       done = true;