Removed gem libraries in mrbc

tools/mrbc/mrbc.rake

@@ -6,7 +6,7 @@ MRuby.each_target do
     objs = Dir.glob("#{dir}/*.{c}").map { |f| f.pathmap("#{build_dir}/%X.o") }
 
     file exec => objs + ["#{build_dir}/lib/libmruby_core.a"] do |t|
-      link t.name, t.prerequisites, [], gems.map { |g| g.mruby_libs }
+      link t.name, t.prerequisites
     end
   end
 end