cpp: integrate Init() into the StartupOptions constructor

This patch integrates the code of Init() function into
StartupOptions's constuctor and thus fixing the TODO
in startup_options.cc.

--
Change-Id: Ic041306387f5ef82fa80d8511c3e9b7be706754a
Reviewed-on: https://bazel-review.googlesource.com/#/c/6332/2
MOS_MIGRATED_REVID=134759417
diff --git a/src/main/cpp/startup_options.h b/src/main/cpp/startup_options.h
index 523523a..b7b4c3f 100644
--- a/src/main/cpp/startup_options.h
+++ b/src/main/cpp/startup_options.h
@@ -207,10 +207,8 @@
 
  private:
   string host_javabase;
-
-  // Sets default values for members.
-  void Init();
 };
 
 }  // namespace blaze
+
 #endif  // BAZEL_SRC_MAIN_CPP_STARTUP_OPTIONS_H_