I do not know much about the plugin. It is a older script I do not know the creator. I could not tell you what it is doing there. But I did read somewhere that putting the double slash will block it out so that it will not show.
You see how the comments are NOT being executed? Generally you would NOT comment code out. If you dont want it, delete it. If you want it make a library. Documenting code can sometimes have its advantages though.
For the sake of explaining it to this guy, I am gonna pretend PHP is compiled.
Okay, so when you run your script, your statements get converted into machine code. However when the compiler see's double slashes then it ignores that line.
Similarly you can comment a "block" by using /* and */. Anything inbetween is not seen by the compiler as runnable code so it skips it.
If your script depends on that statement, then the whole script will fail because now you are NOT executing the statement. Just to be on the safe side, you should uncomment it and use the suggestion given above.
I am assuming your new so you couldnt possibly debug where that variable is being used and how. So just uncomment it. If the script needs it then it will use it, if it dosnt well I think PHP has a garbage collector that will free the memory after.