From what I see, in v2 of GMaps API there was a property \"buttons\" of the InfoWindow object that one could define in a way that given InfoWindow has no close button:
I used the answer given by Tushar Gaurav, but expanded it a little...
$(".gm-style-iw:contains(" + infoText + ")").css("left", function() {
return ($(this).parent().width() - $(this).width()) / 2;
}).next("div").remove();
That will remove the X from an infowindow with the text in infoText, and then recenter the text as it's off-center after removing the close button.
Just adding this for anyone else who stumbles across this page as I did.