[compiler] Remove support for concurrent OSR.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index d67a1d6c385922a439c4a80263ef741789347b2b..c51caf3212529b3a593b456dca8a88b436662f9f 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -996,13 +996,6 @@ class Isolate {
     return optimizing_compile_dispatcher_ != NULL;
   }
 
-  bool concurrent_osr_enabled() const {
-    // Thread is only available with flag enabled.
-    DCHECK(optimizing_compile_dispatcher_ == NULL ||
-           FLAG_concurrent_recompilation);
-    return optimizing_compile_dispatcher_ != NULL && FLAG_concurrent_osr;
-  }
-
   OptimizingCompileDispatcher* optimizing_compile_dispatcher() {
     return optimizing_compile_dispatcher_;
   }